In computing a worm is a self-replicating computer program. It uses a computer network to send copies of itself to other nodes (computers on the network) and it may do so without any user intervention. This is due to security shortcomings on the target computer.

Many worms that have been created are only designed to spread, and don't attempt to alter the systems they pass through..y the network traffic and other unintended effects can often cause major disruption. A "payload" is code designed to do more than spread the worm - it might delete files on a host system (e.g., the ExploreZip worm).

Worms with good intent

Some worms are of good intent e.g my very first research into worms at Xerox PARC, there have been attempts to create useful worms. The Nachi family of worms, for example, tried to download and install patches from Microsoft's website to fix vulnerabilities in the host system – by exploiting those same vulnerabilities. In practice, although this may have made these systems more secure, it generated considerable network traffic, rebooted the machine in the course of patching it, and did its work without the consent of the computer's owner or user.

Protecting against dangerous computer worms

Some worms are spread by exploiting vulnerabilities in operating systems. All vendors supply regular security updates, and if these are installed to a machine then the majority of worms are unable to spread to it. If a vendor acknowledges a vulnerability, but has yet to release a security update to patch it, a zero day exploit is possible. However, these are relatively rare.

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