computer virus

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computer virus,

rogue computer programcomputer program,
a series of instructions that a computer can interpret and execute; programs are also called software to distinguish them from hardware, the physical equipment used in data processing.
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, typically a short program designed to disperse copies of itself to other computers and disrupt those computers' normal operations. A computer virus usually attaches to or inserts itself in an executable file or the boot sector (the area that contains the first instructions executed by a computer when it is started or restarted) of a disk; those that infect both files and boot records are called bimodal viruses. Although some viruses are merely disruptive, others can destroy or corrupt data or cause an operating system or applications program to malfunction.

Millions of computer malware programs are known; they can be spread via removable disks or drives, networks, or Internet websites and services. Although the term virus is commonly used for almost all computer malware, a distinction should be made between a true virus—which must attach itself to another program to be transmitted—and a bomb, a worm, and a trojan (or Trojan horse). A bomb is a program that resides silently in a computer's memory until it is triggered by a specific condition, such as a date. A worm is a destructive program that propagates itself over a network, reproducing as it goes. A trojan is a malicious program that passes itself off as a benign application; it cannot reproduce itself and, like a virus, must be distributed by a USB drive, an external disk, Internet downloads, electronic mail, or the like. Ransomware is a type of malware that encrypts or threatens to encrypt the files on a computer until money is paid, and has become a lucrative form of extortion for organized crime. Malware can also infect advanced cellular telephones (smartphones) and other devices using software. Computer malware has been used since the early 21st cent. to steal sensitive information from government, business, and personal computers and to blackmail computer users. Virus programs that patch programs with security defects that are exploited by malicious computer viruses also exist.

Antivirus programs and hardware have been developed to combat malware. These search for evidence of a malware program (by checking for appearances or behavior that are characteristic of viruses, trojans, and the like), isolate infected files, and remove malware from a computer's software. Researchers are working to sidestep the tedious process of manually analyzing malware and creating protections against each program by developing an automated immune system for computers patterned after biological processes. In 1995 Israel became the first country to legislate penalties both for those who write malware and those who spread the programs.


See F. B. Cohen, A Short Course on Computer Viruses (2d ed. 1994); G. Smith, The Virus Creation Labs: A Journey into the Underground (1994); W. T. Polk et al., Anti-Virus Tools and Techniques for Computer Systems (1995); M. A. Ludwig. The Giant Black Book of Computer Viruses (2d ed. 1998); P. E. Fites, P. Johnston, and M. P. J. Kratz, The Computer Virus Crisis (1999).

virus, computer:

see computer viruscomputer virus,
rogue computer program, typically a short program designed to disperse copies of itself to other computers and disrupt those computers' normal operations.
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computer virus

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Software used to infect a computer. After the virus code is written, it is buried within an existing program. Once that program is executed, the virus code is activated and attaches copies of itself to other programs in the computer and other computers in the network. Infected programs continue to propagate the virus, which is how it spreads.

The effect of the virus may be a simple prank that pops up a message on screen out of the blue, or it may destroy programs and data right away or on a certain date. For example, the famous Michelangelo virus contaminated the machine on Michelangelo's birthday.

Viruses Must Be Run to Do Damage
A virus is a self-contained program that attaches itself to an existing application in a manner that causes it to be executed when the application is run. Macro viruses are similar. The virus code has replaced some or all of the macro commands. Likewise, it is in the execution of the macro that the damage is done (see macro language).

"In the Wild"
The term "computer virus" was coined in the early 1980s, supposedly after a graduate student presented the concept of a program that could "infect" other programs. Since then, more than a million viruses have been defined. However, the bulk of the infections are from only a few hundred active variants, said to be "in the wild."

Since 1993, the WildList Organization has been keeping track of virus attacks around the world. For more information, visit For a sampling of different virus infections, see virus examples. See in the wild, dangerous extensions, quarantine, disinfect, macro virus, email virus, behavior detection, polymorphic virus, stealth virus, worm, boot virus, vandal, virus hoaxes and crypto rage.

Virus Theory
John von Neumann theorized that a computer program could replicate itself in his 1949 paper "Theory and Organization of Complicated Automata," and computer scientist Fred Cohen described the logic for several types of viruses in his 1984 paper "Computer Viruses - Theory and Experiments." See von Neumann architecture.

Windows vs. Mac

Almost all Windows users install an antivirus program in their computers, while many Mac users do not. Windows computers are attacked constantly, because they make up the huge majority of personal computers and are therefore the low-hanging fruit. In addition, the Mac is a Unix-based machine, and the Unix architecture separates the operating system from the applications, which makes it harder to crack, although not impossible. While the majority of Mac users do not use antivirus software, there have indeed been successful virus attacks against Macs, and Mac users are installing antivirus more than they have in the past. See antivirus program.

A Disease - Really?
The concept of a computer "disease" seemed rather foreign in 1989 when this caption from the definition for virus in "The Computer Glossary" was published. Back then, nobody would have believed that millions of viruses were to follow.
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