CSS 211 - Introduction to Network Security

Chapters 1 and 2, Introduction to Security, Malware and Social Engineering Attacks

Objectives:

This lesson introduces the student to basic concepts about the need for computer system security. Objectives important to this lesson:

1. Securing information
2. Definition of terms
3. Types of attackers
4. Formal structure of an attack
5. Five classic defense methods
6. Malware, definition and common types
7. Social engineering: psychological and physical

Concepts:

Chapter 1 begins with some anecdotes about security issues to impress the student with the need for information system security. We might presume that someone who signs up for this class has the idea that such needs exist already. The author presents examples of several ways a computer system might be attacked, compromised, or otherwise damaged. He makes the point that information security is no longer a problem just for IT professionals. All people living in an information rich society are subject to attacks on their IT and financial assets.

• A virus or malware program might be placed in some electronic device that you would not normally consider a threat. Later, it could be used to infect USB sticks that accessed it, making the USB stick a carrier of the virus for any computer it was plugged into later.
• The text discusses a classic "Nigerian email" scam, also known as the Nigerian General or the Nigerian Bank Manager scam. Current events being what they are (changes of leadership in other countries, second half of 2011), I would expect variations on this scam to include Libyan and Egyptian themes sooner or later.
• The text discusses booby trapped web pages; These do not always wait for unwary web surfers, links to them are often included in emails to potential marks (scam victims). Web browsers and personal security programs are including protection from such things, but they are a moving target.
• Specific web based scams use phishing sites. The idea is to get an email recipient to go to a web page, or use email to send sensitive information like login ID and password to the scammer. The mark is supposed to believe that the scammer is actually a trusted authority, like a bank, utility company, or other service vendor. The web addresses used for these sites are often meant to be temporary, so a definitive list must always be changing.
• Customer data is always at risk of being stolen by system break ins. Watch the news for new developments.
• Identity theft is a common fear: you can get a rider for it on your homeowner insurance.
• Theft of laptops holding secure information results in a much worse loss than losing the hardware itself.

In this version of the text, the author pauses to discuss some IT Security related jobs. Larger companies and governmental agencies are likely to employ people in each category, smaller companies are more likely to consolidate security duties in fewer roles.

• Chief Information Security Officer - high level administrator over the other roles, responsible for all security decisions
• Security manager - runs one or more teams of security professionals
• Security administrator - can be a person in charge of a system, or a level of management as the text indicates
• Security technician - the actual worker-level position, this role includes providing support to end users and to system developers regarding security issues

The text also reviews security related certifications, and reminds us that this book is specifically oriented toward the CompTIA Security+ certification.

The text returns to the topic of attacks, and provides some reasons it can be hard to defend against them:

• Speed of attack - interconnected computers pass viruses and worms faster and faster
• Sophistication - attack traffic on a network can look like any other traffic, the attack can morph (change) so it looks different as time goes by
• Simple tools - attack tools are easily available and easy to use: better tools means you don't have to be a good hacker to attack a system well
• Vulnerabilities detected and acted upon - zero day attacks: an attack on a system based on a newly discovered method or newly uncovered vulnerability
  Almost all viruses start out this way. Antivirus programs provide no protection against new viruses until the analysts who write protection and cleaning algorithms know about the virus.
• Lack of timely patching - Delays in patching known issues in software and firmware. Have you noticed that Microsoft, for example, tends to put out patches and updates the 2nd Tuesday of every month? How does that schedule strike you? Often enough, not often enough, or too often?
• Distributed attacks - attacks that take place from many computers at once, typically from already infected or compromised machines.
• BYOD - companies frequently support the Bring Your Own Device to work concept, which sounds like a money saver, but may actually expose company data on an unsecured device
  
• User confusion - the average user does not have a clue whether a security question on a screen is important, much less what the right answer to it might be (The current process is trying to make a change to your system. Do you want to permit this?)

The text turns to a series of definitions that may not seem to apply to all cases. They are general definitions, a starting point to consider what we are working with and working toward.

• information security - the text starts by saying this means guarding digital information. We should remember that some information is also stored on paper, in photographs, and in other media that also need to be protected. The focus of this text seems to be digital information, but the author would surely agree the other media should be secure as well.
• The text also says that security can be viewed as the processes used to defend against attack or as the theoretical result of those processes, the state of being secure.
• The text observes that the more secure a system or device is made, the less convenient it is to use that system or device. This is often seen when rules about passwords change. Users who are forced to use more complex passwords often find some way to remember the password that exposes it to theft (e.g. written on a post-it note).
  

The author discusses the idea that a security program cannot guarantee freedom from attack. The goal is to eliminate or minimize damage from attacks that take place. He provides a justification for providing such protection: to maintain the value of information. He says that there are three aspects of information that are typically protected (CIA) and adds three more (AAA):

• confidentiality - information is accessed only by those who are meant to access it
• integrity - information is correct, and has not been altered except by authorized persons
• availability - information is accessible when needed
• authentication - proving the identity of a user/requester
  
• authorization - providing access to specific assets and resources
  
• accounting - providing an auditable trail of events
  

The text provides a rather long formal definition of information security, and adds three more concepts, three entities that provide protection: products, people, and procedures are what provide the protection. The Products category refers to hardware and software such as firewall devices and authentication software. People would primarily be whoever installs and uses security products. Procedures means plans, policies, and actual steps carried out by those who use information, as well as by those who protect it. I think it is a bit of a reach to have the formal definition include three attributes of information, three ways it is used in a system, and three entities that protect it. This is likely one of those certification question points that we just have to accept as worded the way it is worded, and we aren't allowed to improve it.

The text moves on to discuss more vocabulary, illustrated by a story about a woman who wants to put a new stereo system in her car. The story is useful, but not necessary to understand the terms.

• asset - information that we care about
• threat - a potential form of loss or damage; many threats are only potential threats
• threat agent - a vector for the threat, a way for the threat to occur; could be caused by a person, an event, or a program running an attack
• vulnerability - a weak spot where an attack is possible or more likely to succeed
• exploit - a method of attack; the text calls the act using an exploit to attack through a vulnerability using a threat vector
  
• risk - the probability of a loss; risk can be managed in five classic ways: avoidance, acceptance, mitigation, deterrence, and transference
  

The next section of the text lists several goals of information security that could also be considered as benefits of it.

• preventing data theft - prevention of loss is an obvious benefit of a working security system
• preventing identity theft - this is not necessarily different from the first bullet, since identity information is one kind of data; stolen identity information, however, has a more personal effect on the victims than the simple theft of other corporate data, and provides a means to defraud each victim multiple times
• avoiding legal consequences - those who do not protect their data may be subject to legal charges; the text has a list of several applicable state and federal acts in the US:
  • HIPAA (Health Insurance Portability and Accountability Act), prohibits disclosure of protected health data, with penalties up to $250,000 and 10 years in prison for trying to sell it
  • Sarbox (Sarbanes-Oxley Act of 2002), a reaction to corporate fraud and corruption. It provides penalties up to $5,000,000 and 20 years in prison for officers who file false corporate reports.
  • GLBA (Gramm-Leach-Bliley Act), protects consumer data at banks and financial institutions, provides penalties up to $500,000 for unauthorized disclosure.
  • USA Patriot Act of 2001, authorized law enforcement agencies to obtain documents and data if they have a court order, subpoena, or other authorization; provides several penalties for non-compliance.
  • California Database Security Breach Act of 2003, the first state law requiring that businesses notify state residents within 48 hours of experiencing a data breach of specific personal information data (other states have enacted similar laws).
  • COPPA (Children's Online Privacy Act of 1998), federal act that requires entities to get parental permission before collecting, using, disclosing, or displaying data about children under 13 (no penalties stated in the text).
• maintaining productivity - prevention saves the effort (time and cost) that a successful attack would incur.
  The text implies that in the case of an attack, you should estimate that it will take about 1% of your total staff to combat the attack.
  The cost of virus attacks includes cleaning cost, loss of productivity, and loss of revenue. Follow this link to a list of ten famous and expensive viruses.
• foiling cyberterrorism - the potential for terrorists to disrupt a national infrastructure includes disruption of health and emergency services, power, communications, and commerce.

The text discusses some categories used to classify attackers:

• hackers - One of the buzzwords of computer system geeks, this one can mean anything; it is generally accepted to mean someone with more skill than an average user, may be a white hat (good guy) or black hat (bad guy). A hacker may break in to a system for a thrill, to show off, or to cause some kind of damage. The text also throws in the concept of a gray hat, a hacker who will find a vulnerability and announce it to the public instead of telling the vulnerable institution.
  
• script kiddies - attackers who use hacking tools that they don't really understand
• brokers - hackers who find vulnerabilities and sell the information; the text says "to the highest bidder" but the information may actually be sold multiple times
  
• spies - computer attackers who are looking for specific data from specific systems
• employees/insiders - Computer security includes the concept of protecting data from people who aren't authorized to access it. What about protecting it from authorized users who want to give or sell it to someone else? What about authorized users who give out their password because someone asks for it? What about users who are no good at protecting their secrets?
• cybercriminals - The text has a longer discussion of this category. The bottom line is that they are after some financial gain. This could be data they can sell, actual fund transfers, or theft of financial instruments.
• cyberterrorists - A cyberterrorist is defined as a system attacker whose motivations are ideological.
• hacktivists - hackers who disable or deface a web presence to make a political point
• state sponsored attackers - government supported attackers (who may work for an agency or an armed service of that government)
  

The text lists seven steps that an attacker may follow in preparing for and carrying out a computer system attack:

1. Probe for information - look over the target and find potential weak spots; for example, look for open ports on servers
2. Weaponize - create an exploit based on what you found
   
3. Delivery - penetrate defenses; actually stage the attack, whether by email, attempted login, or other means
4. Exploitation - execute the element that was delivered to the target
   
5. Installation - may mean to install a back door for future entry, or to put code in place for execution
6. Command and control - optional step, the exploit code contacts the attacker to begin a download or to provide a control interface
7. Actions on objectives - the attack harvests data, does damage, creates a zombie, or whatever the attacker wished to accomplish

Consider that not all attackers will follow all of these steps. Some would damage a system without making a back door for later, some would explore a system but never damage it, and others might steal data to make public what the data owners would rather be secret.

The author also gives us five defenses against attacks.

• layering - the author spends more time with metaphors than with examples; the point is just that a security solution will have multiple layers, requiring an attacker to get through several kinds of protection before accessing data
• limiting - it is a standard feature of most databases that the designer can restrict users to specific views of the data, letting them see only what their role requires, letting only specific authenticated users modify or add information to the data files; network security can be like this as well, offering only role or user specific views of data, only allowing limited changes by specific users
• diversity - diversity should be part of the layering concept, but that would mean we would need another bullet; diversity means that each layer of security is different in some way from the other layers, so an attacker will not be able to use the same exploit to get through all the layers
• obscurity - this means that the inner workings of the system should not be described or stated where a potential attacker could access that information; As a network system user, this is one of the more irritating aspects to me. Consider passwords. The network tells me my password will expire, and offers me a chance to change it now. I offer it a new password, and it replies that the new password is too short. I offer another one, and it tells me I haven't used enough complexity (upper case, lower case, numbers, and symbols: use at least one from at least three types). I offer another, and it tells me I can't use a password I used as recently as 10 changes ago. You see the pattern? Let there be rules for using the system, but the user is not made aware of the rule until it is violated. In the case of securing the system from attackers, the attacker is not told any of these rules when they are trying to guess a password.
• simplicity - let the system be simple to administer, but hard to hack

Chapter 2 is titled Malware and Social Engineering Attacks. It begins with an article that describes one sort of social engineering attack. The attackers (actually researchers) created accounts on Facebook and LinkedIn for a fictitious, attractive, female MIT graduate who supposedly worked in the IT security industry. The key to this approach was to make the lure believable, and to gain trust, and to ask for nothing at first. Eventually, male employees at a targeted security agency clicked on a link that loaded an executable to their computers, and the researchers gained access to the targeted system. It is interesting that when the project was tried in reverse, posting accounts with a fictitious male lure in search of female responders, there was no success. Perhaps the male lure should have been constructed by female researchers, or maybe the male employees who were duped should learn some things about women?

The author explains that most successful attacks contain elements of malware and social engineering. He states that "tricking the users into performing a compromising action" is the most cost effective approach to staging an attack. The story at the start of the chapter is not just entertaining. It is a cautionary tale, which should impress would-be professionals with the fact that they should act like professionals.

The term malware is introduced in this chapter. It means any software that does something harmful to a system. The text breaks malware into types by several methods. The author remarks that malware is often detected by its signature, the way its files are named, coded, or deployed. Malware authors know this, and have taken three approaches to avoiding this kind of detection:

• oligomorphic - the program contains several versions of its code, each a bit different from the others; each time it executes, it can use one of these different versions of itself, but it will eventually repeat a version
• polymorphic - the deployed version of the malware contains code that is scrambled/encrypted/camouflaged, that must be unscrambled before it is executed; in this way, the deployed package does not resemble the actual attacking package
• metamorphic - the package rewrites its code when it is executed, making a new version of itself each time that will not be identical to known versions

The author then discusses malware at length, based on whether it falls into one of three (four?) types, which are based on the objectives the malware follows: circulating/infecting a system, concealing its actions, or bringing profit from its actions by its payload.

Circulating/Infecting Malware

The text lists circulating and infecting as two types of malware, but they are discussed as one. Infecting software is divided into viruses, worms, and Trojans. A virus typically requires a carrier to infect a system, like an email, an instant message, or a program that the user runs. A virus typically has two tasks: replicate and damage. Some viruses have historically been rather benign, just displaying a message to the user. The ones that cause damage to a system are categorized by the method they use or the damage they cause:

• appender - an older type that writes its malicious code to the end of an existing program (appends to it), and places an instruction at the beginning of the program that skips all the original program code, and executes the virus code instead of the desired program code; this is also called a file infector
  The text offers two variants on this type:
  swiss cheese infection - the virus code is encrypted until it is run, and the decryption engine (code) is stored in several segments in the infected file
  split infection - the virus code is encrypted, like the version above, but the entire malware program is broken into pieces, stored in various file segments, and linked together when needed
  
  Earlier versions of the text also listed these virus types:
• resident (aka terminate and stay resident) virus - loads into RAM, then does its damage based on actions the user takes through the operating system
• boot virus - infects the Master Boot Record of a hard disk, which means the virus will load and run the next time the hard drive is used to boot the computer; typically the virus will trash the hard drive
• companion virus - found more on pre-Windows systems, loads a program with a name similar to that of a real program, but with a preferred extension so the companion (malware) program is run when the user tries to run the real program from a command line; this seems like it might have a resurgence in Windows Server 8 which has more command line features
• macro virus - a script virus that is typically placed in a Microsoft Office file

Virus protection programs typically recognize viruses by signatures, the way they look. This recognition method is complicated by metamorphic viruses that change the way they look over time, and polymorphic viruses that change their signature and their encryption methods.

Worms are described on page 57. The text tells us a major difference between worms and viruses: once it is started, a worm can replicate itself across connected computer systems without further human interaction. It does not need a carrier. A worm can attack any running computer that is connected to a network that an infected computer is on: it does not require cooperation from the user. Worms are more dangerous due to their self driven nature. Once a worm is detected in a system, each device on the network must be scanned for it, cleaned if necessary, and prevented from accessing the network until this is done.

Trojan horse programs are named for the myth of a wooden horse that was used to smuggle Greek soldiers inside the walls of Troy. A program of this sort has two aspects: what we are told it does, and what it actually does. In some cases, Trojans may do what they say, but they also have a hidden malicious purpose which is what puts them in this category. A classic ploy used by Trojans is to pretend not to be a program at all. The text gives an example of a file that has a .exe extension, but the characters .docx occur in the name immediately before it. If a Windows computer is using the default (idiotic!) configuration, the actual .exe extension will be hidden from the user, and the user may think it is only a Word document.

Concealing Malware

The text discusses one type of malware whose first concern is remaining hidden from the user and from security personnel:rootkits. At first, a rootkit sounds like a resident virus that replaces operating system files with its own. There are similarities, but one difference is that a rootkit is much more extensive, and another is that the rootkit obtains elevated privileges to carry out its stealth actions. The resident virus may replace one program on the computer, which will then do some harm to the system. The rootkit opens a door for lots of malware. How?

Have you ever seen a movie about a robbery in which the robbers send false information to security staff (like a video loop) that shows all is well, while the robbers proceed to steal whatever they want? That's kind of what a rootkit does. The rootkit assumes the role of a trustworthy part of the operating system. It will stand between the user and security software on one side, and other malware doing whatever it wants on the other.

The intention of the rootkit programmer may not be malicious. Of course, that is possible with any program, but our concern here is about malware. The text discusses the example of Sony, who in 2005 put a rootkit installer on several of their audio CDs. The rootkit had the goal of preventing computer users from copying those CDs. Sony's intent was not malicious, but their rootkit changed a PC without the user's consent, and it made the PC vulnerable to security exploits. The first is just wrong, and the second is worse. As the saying goes, the road to hell is paved with good intentions.

Detection and removal of a rootkit can be difficult, but it is worth trying before following the text's scenario of formatting the hard drive and starting over. The Sophos company, for example, has a free download that is supposed to be good at finding and removing these problems. Here is another one from Kaspersky. Students should do an internet search for tools from the vendor of their choice.

Privilege escalation is a technique, not a type. The technique is commonly use by system administrators. They log in to networks with an ID that has normal privileges on the system, but they execute administrative tasks with an ID that has elevated privileges. Of course, these are authorized users who are supposed to do such things. When malware does this, it may do it in one of two ways. It may use an exploit to escalate its own privileges, or it may access the privileges of another account which are greater than its own.

Malware for Profit: Malware Noted by Its Capabilities

The text discusses some major and minor types in this category. The first is Spyware, described on page 60. It is defined as software that violates a user's security. More informatively, the text says that spyware typically has one of four missions: to install other software without the user's consent, collection of personal information such as browsing history, changing configuration settings, or collection of private information for sale or for the commission of fraud. The text proposes that if other software did what spyware does with the user's permission, that software would not be spyware. So the issue is not what it does, as much as the fact that it is done in secret, without the user's "notice, consent, or control".

A subcategory of spyware is keyloggers. Keyloggers can be implemented through hardware or software. The idea is that the program (or device) captures every key press the user makes, which can be analyzed later for by someone who reads the key log. Obviously, capturing IDs and passwords would be one use of such a product. Keeping a log of all activity on a computer would be another. Some viruses contain a key logging function which sends its log to the virus originator.

The chart on page 60 lists effects that spyware can have on a computer. Several of these items seem to be less related to spying than to leading the user to particular products and resources. As such, I would consider "spyware" to be an inappropriate label for the category. A better label is the next subcategory the text talks about, adware.

As its name suggests, adware is concerned with presenting advertisements to the computer user. Adware is universally disliked. At best, it presents an interruption or a distraction to the user. At its worst, it can crash programs or the operating system.

On page 62, the author discusses ransomware, which is described as software that disables or locks your computer until you pay a ransom to the hacker who created or exploited your computer with it.The infecting program may pretend to be from a government agency, an anti-virus company, or some other recognized and trusted source, which convinces a small percentage (3%) of computer users that they should pay the requested fee to have their computers cleaned of the "detected problem".

Deleting data is another common payload capability. The text mentions logic bombs on page 64, another type of concealed malware, as an example of malware that will delete data. A logic bomb is not a bomb. It is malware that waits for a logical condition to occur before it executes its mission. A classic case was the Michelangelo virus that only executed on the birthday of Michelangelo Buonarroti (which, as everyone knows, is March 6th). In other examples, some act like "dead man switches", where the malware engages if it is not regularly reset, or if a person's ID is removed from a network. A logic bomb can be hidden in a much larger program, making it difficult to find. It is also possible for a logic bomb to take actions other than deleting files.

Another payload effect is modifying system security. Disgruntled system administrators have been known to leave logic bombs in their own systems set to change security settings if they are not removed or reset by an arbitrary date. The intention is to disable the system if the administrator is not allowed to continue to manage the system. When a modification program is placed on a system by an attacker, it is more likely being done to open a back door, a new account that has elevated permissions which will give the attacker all desired access to the system.

The text notes that program developers may install back door access for themselves, to be used while the system is being developed and debugged. This is not malicious. It is an efficient means to access, repair, and improve the system. These back doors are not commonly left in place in the deployed versions of the programs, but they may be, which presents a vulnerability to attack.

The last payload category is one that will launch an attack. As a current example, the text discusses the concept of a botnet. This has been around for a while, but it is a refinement and step back from the others at the same time. A botnet is a network of computers that have been infected, turned into robots (aka zombies), that can be used for any kind of attack. The refinement is the creation of a network of infected machines on one mission. The step back is the brute force aspect of the attacks. The attacker (the bot herder) does not depend on finesse or subtlety, he uses more points of attack to meet his goal. Four types of botnet attacks are listed on page 66.

• spam - Botnets can follow a script to send spam faster than an individual system can.
  
• spreading malware - When an infection is being spread by a coordinated attack from a botnet it is much harder to stop.
  
• poll (election) manipulation - Each zombie pretends to be one or many devices, changing the results of online voting.
  
• denial of service - Any network can be disabled by too many requests, which is an easy attack for a botnet to stage.
  

Social Engineering Attacks

The text returns to social engineering on page 66. It begins with another story about people simply asking for access to a building and an office, and making a request for a password change. A primary aspect of social engineering is all about asking people for information they see no reason to keep secret.

Psychological Approaches

The table on page 67 lists six attitudes/approaches the social engineer might take when making a request for a password change.

• authority - pretend to be someone who has the right to make the request
• intimidation - in an oppressive environment, it may be easy to use fear of what would happen if the request is not granted
• consensus/social proof - tell a believable lie that others have granted this request in the past
• scarcity -  tell the victim that you are short on time, or you have to get this before it can't be done
• urgency -  tell the victim that you need this right now, and that you will complete the red tape later
• familiarity/liking - act like one of the family, especially one who appreciate the work the victim does for the company
• trust - use details about the organization to make it seem like you are a part of it
  

Someone who is practiced in manipulating people may be able to choose between these approaches easily, based on the attitude of the person on the other end of the phone, email, or messaging application.

The text mentions that basic information about target or a work site may be obtained from documents on a public facing website, a Facebook site, unshredded trash, or a phone call to the right person. More advice is offered on page 68:

• ask for a little information from each of several people, building your required knowledge base without alerting the victims
• ask for what the victim is likely to be able to provide; don't ask for something inconsistent with the victim's job or role
• be pleasant and flattering, but in moderation
• don't ask for so much that it raises suspicion about you
• asking for help often triggers sympathy, thanking the victim helps them believe they have done something good
  

The text continues with a discussion of several other approaches under this heading.

• impersonation - An attacker might impersonate anyone who might seem to belong in the environment being surveilled or attacked. It is common to impersonate a help desk employee when calling a victim. It is also common to impersonate an employee, a delivery person, or a repair person when the ploy calls for infiltrating a site.
  
• phishing - Phishing is the solicitation of personal or company information, typically through an official looking email. Some variations on phishing:
  • spear phishing - sending the email to specific people, customizing it to look like a message sent to them by an entity with some of their personal information already
  • whaling - This is spear phishing but it focuses on big (wealthy or data rich) targets.
    
  • pharming - sending an email that takes the person dddirectly to a web site (the phisher's site) instead of asking the reader to follow a link
  • Google phishing - the phisher sets up a fake search engineee that will send people to the phishing web site on specific searches (presumably it returns real search results on searches that would not lead to a page the phisher has prepared)
• spam - The section on spam, unsolicited email, seems out of place in this discussion. Most spam may only be looking for a customer, but some spam is sent with the intent to steal, abuse, and sell the payment information that a person might volunteer to provide.
  
• hoaxes - In the larger sense, all social engineering involves a hoax of some kind. First the grifter finds a mark, then he tells the mark the tale, and offers the deal. In the sense that the text means here, a hoax is distraction from reality, such as when the attacker pretends that there is a virus outbreak that is affecting the potential victim. It sets the idea in the victim's mind that the attacker is trying to help and should be assisted in his/her efforts.
  
• typo squatting - Most people are not great typists. The tttext explains that this is why other people (the bad ones) register domain names that are similar but not identical to real domains. They are hoping that the bad typists among us will misspell a URL and find ourselves on their site instead of the one we wanted, where we might volunteer information by trying to log in with credentials that can then be abused, sold, or ransomed. This technique is also called URL hijacking by the text.
  
• watering hole attack - The attacker determines that targets in the company/agency often visit a particular web site, called the watering hole in this scenario. It may be easier to infect that site than to attack the individuals directly, and then to take advantage of the real target.
  

Physical Approaches 

• dumpster diving - Attackers doing research on a company caaan learn a lot from the trash the company discards. The text provides a table on page 73 with seven suggestions about things to look for in a target's trash.
  
• tailgating - The concept behind tailgating is simple. Someone who does not have authorization to pass through a secure entry point will gain access by simply following an authorized person through it, or by waiting for the door to open as someone exits through it. This might be done with or without the knowledge or cooperation of the authorized person.