A virus is a piece of programming code usually disguised as something else that causes some unexpected and usually undesirable event. A virus is often designed so that it is automatically spread to other computer users. Viruses can be transmitted as attachments to an e-mail note, as downloads, or be present on a diskette or CD. It is important to have updated antivirus software so that the newest viruses and worms will be detected and halted.
A virus is a piece of programming code inserted into other programming to cause some unexpected and, for the victim, usually undesirable event. Viruses can be transmitted by downloading programming from other sites or be present on a diskette. The source of the file you're downloading or of a diskette you've received is often unaware of the virus. The virus lies dormant until circumstances cause its code to be executed by the computer.