Home > Articles

0672318717

  • Print
  • + Share This
sams_sample_chap

Chapter 17: Viruses and Worms

Do you have a virus? No instruments, no senses can tell you if you are in the presence of the predator.

—Richard Preston, The Hot Zone

If doctors and pharmacists worked like anti-virus vendors, we'd all be immunized against all illnesses. Would this improve our viability as a species?

—David Harley, Icarus

This chapter addresses one of the best-known, most-feared and least-understood problems in information security. It explains what viruses and worms really are (and aren't), summarizes the means of limiting their impact, and, most importantly, includes some pointers to further information.

Understanding Viruses and Worms

Computer viruses are perhaps the most well known and feared security threats of all. Certainly, they're among the most misunderstood. All viruses entail a certain degree of damage, but their impact, with some very prominent exceptions, is mostly social.

Every virus does cause some (usually) limited denial of service because they all steal disk space, memory, and/or clock cycles (processor time). Some cause unintended (accidental) damage on some systems. Some do intentional damage to files and file systems, and a few can make some hardware effectively unusable by trashing firmware (CIH, for example). At this time, no known virus directly damages hardware, although the possibility of such a virus can't be discounted. However, some of the most successful viruses (in terms of survival) achieve longevity by virtue of the fact that they do nothing but replicate and therefore aren't conspicuous. Direct damage tends to be noticeable. However, some viruses cause serious damage to data by slow and insidious corruption, and others continue to survive despite their high damage profile.

It has to be said even an innocuous virus can cause problems just by being there, or even by being misdiagnosed as being there. This can result in secondary damage because of inappropriate action taken by poorly informed virus victims. It can also result in social damage. Such damage can include loss of reputation, scapegoating of the victims of a virus attack, or even legal action. A victim might be accused of failing to apply "due diligence," of being in breach of contract, or of being in contravention of data protection legislation. He might even be accused of implication in the dissemination of a virus, which is illegal in many countries (even those in which the actual creation of viruses is not in itself a crime).

Viruses that do no intentional damage are sometimes described as benign, in much the same way that a tumor might be defined as malign or benign. However, this usage is potentially misleading because the use of benign in this context does not mean harmless, let alone benevolent, as it might be understood to mean.

The meteoric expansion of Internet usage (especially email) since the early 1990s has raised the status of the virus from an occasional nuisance to everyone's problem. The vastly increased use of local networks and other means of sharing data and applications has also increased the risks by orders of magnitude. In brief, viruses can travel further and faster than was the case a few years ago. The big comeback story in the virus field is that of the computer worm. In the early 1990s, Internet usage became less specific to "big iron" mainframes and minicomputers reached via dumb terminals and terminal emulators. The first generation of worms declined in impact accordingly. Virus and anti-virus technology became focused on the individual desktop PC. In the latter part of the decade, however, virus writers began to rediscover worm mechanisms as a means of accelerating dissemination, until worms and worm/virus hybrids have now become one of the most aggravating problems faced by systems administrators.

This chapter, although it addresses worm mechanisms is some detail, isn't particularly focused on differentiating between viruses and worms. Even within the industry, the terms are often used interchangeably in the context of the hybrid viruses/worms that dominate the current virus scene.

What Is a Computer Virus?

Most anti-virus professionals would accept a working definition of the term computer virus like this: "a program that replicates by 'infecting' other programs so that they contain a (possibly evolved) copy of the virus." (F. Cohen: A Short Course on Computer Viruses.)

Note that the emphasis here is on reproduction by infection. A virus is not per se destructive, whereas a destructive program is not per se a virus. Furthermore, although most viruses do attempt to operate without the knowledge of the system user, this isn't a requirement either. The only defining characteristic is replication: the primary 'intent' of the infective program is to reproduce.

NOTE

The term program does not necessarily imply a program file, although, most viruses do in some way infect files. Nevertheless, we refer to infected and infective objects in this chapter unless we are specifically considering file infection, so as to include boot sector infectors and macro programs embedded in data files.

Infection is sometimes described in terms of attachment of the viral program to one or more programs on the target system. However, attachment is perhaps a misleading term, although it is conventionally used in this context because the word attachment has a rather different connotation in the context of email. It might be more useful to look at the process in terms of a chain of command. The viral code is inserted into the chain of command so that when the legitimate but infected program is run, the viral code is also executed (or in some instances, runs instead of the legitimate code).

We often describe infection in terms of the viral code becoming physically attached to the host program, but this isn't always the case. Sometimes, the environment is manipulated so that calling a given program calls the viral program. Sometimes, the viral program is activated before any program is run. This can effectively "infect" every executable file on the system, even though none of those files are actually physically modified. Viruses that take this approach include cluster or FAT (File Allocation Table) viruses, which redirect system pointers to infected files; companion viruses; and viruses that modify the Windows Registry so that their own code is called before legitimate executables.

Except for a few extraordinarily primitive and destructive examples that actually trash the host program on infection, all viruses work along these lines:

  • A computer user calls a legitimate program.

  • The virus code, having inserted itself into the chain of command, executes instead of the legitimate program.

  • The virus code terminates and hands over control to the legitimate program.

Companion or spawning viruses follow the same sequence, but the virus code is contained in a separate file, which is (characteristically) renamed so that it will be executed instead of the program the victim thought he was launching. (It then normally hands over control to the legitimate program.)

The virus process is a little like the process of biological viral infection, although the analogy is overworked and can be misleading. Think of a person infected with an airborne disease. Whenever he exhales in a public place, he risks infecting others. Similarly, whenever an infected program is executed, the virus's infective routine also runs, and can infect one or more other objects "in range". Just as biological viruses infect hosts that are predisposed to infection, computer viruses target certain type of files and system areas, according to virus type.

What Is a Computer Worm?

Replication is also the defining characteristic of a worm, and some authorities (including Fred Cohen, the "father" of computer virology) regard worms as a subset of the genus virus. However, worms present particular problems of definition. One viable definition distinguishes between worms and viruses in terms of attachment. Whereas a virus in some sense "attaches" to a legitimate program, a worm copies itself across networks and/or systems without attachment. It can be said that the worm infects the environment (an operating system or mail system, for instance), rather than specific infectable objects, such as files.

Some observers have used the term worm to refer to self-replicating malware (MALicious softWARE) that spreads across networks. This doesn't really amount to a meaningful distinction because many viruses can travel between machines on a Local Area Network, for instance, without being "aware" that a target volume is not on the same machine. This isn't to say, of course, that viruses are never network aware.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020