sgtbham
Rock Crawler
Basically, it means that hackers can use your PC to attack websites and things like that. They attack websites by having soo many PCs hit them at once that the servers cant keep up, which shuts down the website. If you are part of a botnet your computer is one of the ones bombarding the website under attack, but there are a ton of other things that not having anti-virus leaves you open to. Its just a good thing to have.