Worms, Trojans, Spyware

Malware: a general class of bad (malicious) software. Malware includes types including:

Worms | Trojan Horses | Spyware | Viruses

Worms

A computer worm is a self-replicating (it can make copies of itself) malware (evil-doing) self-sufficient computer program. It uses a network to send copies of itself to other computers without any user intervention. Transport is often achieved by email attachments.

Unlike a virus, it does not need to attach itself to an existing program. Viruses are now actually rather rare. Most infections now are from worms.

Many worms are designed to simply spread themselves, but even at this very lowest level of threat, worms are bad for a network and a computer because of the extra bandwidth they consume. In serious cases like the Mydoom worm, severe network degradation can result.

Payload: A "payload" (a term adopted from a bomber's bomb capacity) is code in the worm that does more than just distribute itself. It might:

• delete files
• encrypt files in a cryptoviral extortion attack (where victims' files are made accessible again only if a ransom is paid)
• send sensitive documents
• install a backdoor in the infected computer to let it be remote-controlled by the worm's author to participate in a botnet DDOS (Distributed Denial Of Service) attack, or sending floods of spam.
• install a keylogger which records all keystrokes (including bank account logins, credit card information, site passwords etc) and mails them back to the worm's author.

Worms usually gain entry to a computer by exploiting vulnerabilities in the host's operating system. Constant OS updates are needed to head off such exploits.

Phishing emails often get an unsuspecting user to download and open a worm. Typical methods are to open an attachment, view a supposed 'e-greeting card', or visit a website that hosts the worm.

The term "worm"' was first used in John Brunner's 1975 novel, The Shockwave Rider in which a man designs and sets off a data-gathering worm in an act of revenge against the powerful men who run a national electronic information web that induces mass conformity.