For example, a virus may be designed to conceal itself until a predetermined date, then flash a message on all network computers. 'Some viruses are high-tech pranks not intended to cause damage. It waits until triggered by some pre-set event or date and then delivers a payload that may include destroying files or disks. A Trojan Horse masquerades as a legitimate software program. A logic bomb is a program normally hidden deep in the main computer and set to activate at some point in the future, destroying data. A computer worm spreads like a virus but is an independent program rather than hidden inside another program. 'Worms, logic bombs, and Trojan Horses are similar 'infections' commonly grouped with computer viruses. A virus is only one of several types of 'malicious logic' that can harm your computer or your entire network. Like a real virus, it can reproduce, infect other computers, and then lie dormant for months or years before it strikes. 'A virus is a small, self-contained piece of computer code hidden within another computer program. Derived From: Viruses and other Infections, Dept of Energy

Google worm virus