According to Wikipedia, "Malware" is: "software designed to infiltrate or damage a computer system without the owner's informed consent."
In today's technology tip we have some definitions of the names you might have heard for various kinds of malware.
computer viruses - a computer program that can copy itself onto a computer without the permission or knowledge of the user (complete wikipedia definition). Viruses could be introduced to your computer from a disk, flash drive, CD.
computer worms - Similar to a computer virus but a worm can "Self replicate" itself to other computers throughout a computer network without any user involvement. Complete wikipedia definition.
trojan horse - Just like the mythological Trojan Horse, these programs appear to be useful free downloads but when you download them to your computer you also download other unwanted and malicious programs onto your computer (complete wikipedia definition). Trojans could thus be used to install all kinds of malware onto your computer.
spyware - Malware that is downloaded to your computer with the purpose of tracking or recording the user's activities without the user's consent (complete wikipedia definition). Such malicious software could be used to log keystrokes to get passwords, or just track internet search histories to target pop-up advertisements.
adware - Some free downloads from the internet will ask the user for consent to install spyware software on the users computer as part of the download agreement. Such software is usually referred to as adware instead of spyware since the user has given consent to be tracked in exchange for some free software.
How to clean malware off your computer?
For starters, here's a popular free download for finding spyware on your computer: Ad-Aware from Lavasoft: http://www.lavasoftusa.com/
They have a free version that you can try.
Then there's the anti-virus software you can buy. Here's a review of the Top Antivirus Software from PC World: