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Malware - Infectious malware: viruses and worms

Malware - Infectious malware: viruses and worms: Encyclopedia II - Malware - Infectious malware: viruses and worms

The best-known types of malware, viruses and worms, are known for the manner in which they spread, rather than any other particular behavior. Originally, the term computer virus was used for a program which infected other executable software, while a worm transmitted itself over a network to infect computers. Today, the words are often used interchangeably. Today, some draw the distinction between viruses and worms by saying that a virus requires user intervention to spread, whereas a worm spreads automatic ...

Malware: Encyclopedia II - Malware - Infectious malware: viruses and worms

Malware - Infectious malware: viruses and worms

The best-known types of malware, viruses and worms, are known for the manner in which they spread, rather than any other particular behavior. Originally, the term computer virus was used for a program which infected other executable software, while a worm transmitted itself over a network to infect computers. Today, the words are often used interchangeably.

Today, some draw the distinction between viruses and worms by saying that a virus requires user intervention to spread, whereas a worm spreads automatically. This means that infections transmitted by email, which rely on the recipient opening an attachment to infect the system, are classed as viruses.

Malware - Capsule history of viruses and worms

Main articles: Computer virus, computer worm.

Before Internet access became widespread, viruses spread on personal computers by infecting programs or the executable boot sectors of floppy disks. By inserting a copy of itself into the machine code instructions in these executables, a virus causes itself to be run whenever the program is run or the disk is booted. Early computer viruses were written for the Apple II and Macintosh, but they became more widespread with the dominance of the IBM PC and MS-DOS system. Executable-infecting viruses are dependent on users exchanging software or boot floppies, so they spread heavily in computer hobbyist circles.

The first worms -- network-borne infectious programs -- originated not on personal computers, but on multitasking Unix systems. The first well-known worm was the Internet Worm of 1988, which infected SunOS and VAX BSD systems. Unlike a virus, this worm did not insert itself into other programs; rather, it exploited security holes in network server programs and started itself running as a separate process. This same behavior is used by today's worms as well.

With the rise of the Microsoft Windows platform in the 1990s, and the flexible macro systems of its applications, it became possible to write infectious code in the macro language of Microsoft Word and similar programs. These macro viruses infect documents and templates rather than applications, but rely on the fact that macros in a Word document are a form of executable code.

Today, worms are most commonly written for the Windows OS, although a small number are also written for Linux and other Unix systems. Worms today work in the same basic way as 1988's Internet Worm: they scan the network for computers with vulnerable network services, break in to those computers, and copy themselves over. Worm outbreaks have become a cyclical plague for both home users and businesses, eclipsed recently in terms of damage by spyware, for which see below.

Other related archives

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Adapted from the Wikipedia article "Infectious malware: viruses and worms", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki

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