What's the Difference Between Virus, Spyware and Adware?

Computer malware is usually divided into virus, spyware, adware, Trojan horses, worms and rootkits.

Virus is a tiny program that can cause damage to your files, operating system or even hardware. Viruses are designed solely to bug you or to destroy your work.

Spyware is spying software designed to track your activity, record the keystrokes you type or passwords you send over to Websites. Spyware can steal your email passwords, online banking passwords, or credit card numbers.

Adware is designed to display unwanted ads in form of a pop-up window either on your desktop or in the Web browser window.

Trojan horses aka backdoors are used by malicious people to gain full access to your computer without your prior consent or knowledge. A successful Trojan attack is one of the most dangerous attacks, because there is live hacker out there doing harm to you in an intelligent way.

Worm doesn't necessarily do you any harm, but it's likely to consume your Internet bandwidth and slow your PC a lot.