I get this question a lot. Here is a great breakdown of malware I found on http://www.seas.ucla.edu/security/malware.html
How to Protect Against Malicious Software
What is malicious software?
Malicious software (malware) is any software that gives partial to full control of your computer to do whatever the malware creator wants. Malware can be a virus, worm, trojan, adware, spyware, root kit, etc. The damage done can vary from something slight as changing the author's name on a document to full control of your machine without your ability to easily find out. Most malware requires the user to initiate it's operation. Some vectors of attack include attachments in e-mails, browsing a malicious website that installs software after the user clicks ok on a pop-up, and from vulnerabilities in the operating system or programs. Malware is not limited to one operating system.
Malware types can be categorized as follows: viruses, worms, trojans, and backdoors seek to infect and spread themselves to create more havoc. Adware and spyware seek to embed themselves to watch what the user does and act upon that data. Root kits seek to give full access of your machine to the attacker to do what they want.
What can I do?
SEASnet does not have any anti-spyware/anti-adware software. However, there are many anti-spyware/anti-adware programs available on the internet. Here is a list of a few of them:
*Some websites require Internet Explorer to work properly. If the alternate web browsers do not work for these websites, then fall back to using IE.