virus

In computing, a piece of software that can replicate and transfer itself from one computer to another, without the user being aware of it. Some viruses are relatively harmless, but many can damage or destroy data. Antivirus software can be used to detect and destroy well-known viruses, but new viruses continually appear and these may bypass existing antivirus programs. The earliest was the Brain virus, written in Pakistan in 1986.

Viruses are written by anonymous programmers, often maliciously, and are spread on the Internet, on floppy disks, CD-ROMs, and via networks and e-mail attachments. Viruses may be programmed to operate on a particular date. Most viruses hide in the boot sectors of floppy or hard disks or infect program files.

Since 1995 there have also been macro viruses that infect Microsoft Word or Excel. The first of these were the Concept virus (infecting Word files) and the Laroux virus (infecting Excel).

In 1999, the Melissa virus caused an estimated US$80 million worth of damage, with LoveBug causing US$7 billion worth and affecting about 45 million computers the following year. In 2003, Slammer caused cash machines to crash and delayed airline flights, while SoBig and Blaster exploited weaknesses in the Windows 2000 and NT operating systems. Most recent viruses are actually worms, which replicate themselves over the Internet.

A recent ploy is to use ‘social engineering’ - such as the pretence of the message having come from a reputable company, or to be reporting a failed attempt to send an e-mail - to trick the recipient into opening the attachment containing the malicious code.