The computer virus is one of the best known threats to your PC. However, the name 'virus' is not applicable to every threat. Every class has its own name. Often, the various classes are being mixed-up without really knowing the differences between them. The definitions below will help you to tell one from the other.

Virus

A virus attaches itself to the code of other programs it has contact with, like parts of Windows or Internet Explorer. Every time you start the infected program, the virus is activated as well without you knowing. Viruses replicate themselves and may cause damage to programs or user files.

Worm

Worms are programs that replicate themselves from system to system without the use of a host file, for instance by sending e-mails with the worm's code in an attachment. A worm can cause damage and may compromise the security of your computer. The worm gains access by using a weak spot on the system or when a user opens an infected e-mail.

Trojan horse

A Trojan horse is an impostor that claims to be something desirable but, in fact, is malicious. Trojan horses do not replicate themselves, but cause damage or compromise system security. A Trojan horse has to be sent by somebody else or is being installed by the user as part of a trusted software package. Damaged files or giving others access to your computer, are some of the harmful activities of Trojan horses.

Spyware

Spyware collects information about users' browsing activity, preferences, interests and personal data. The information collected is sent to the creator of the application or to third-parties, and can be stored in a way that it can be recovered at a later time. Spyware tries to collect usernames, passwords, PIN numbers, credit card numbers and information on your identity.

Adware

Adware is the class of programs that display advertising using any means. Often, they use annoying pop-ups trying to get you to visit certain websites. Most of these websites offer services, which you have to pay for.

Keylogger

A keylogger collects personal information by capturing every key pressed by the user and send this to the e-mail address of its creator. This way anything you key in like usernames, passwords, PIN numbers, credit card numbers etc. can come in the hands of third parties.