There can't be anybody in the world today that hasn't heard of computer viruses in some shape or form, hence that's why it is essential that every PC user should have an anti-virus program of some sort or another installed on their machine.

Doesn't slow your machine down. Does a good job of detecting viruses and dealing with them.

It has all the essentials, including a resident memory scanner, an e-mail scanner, and scheduled hard disc scans.

Easy to install. After downloading the setup program and clicking on in, you just need to click a couple of buttons ie: Next and Next, and that's it, before you know it AVG is installed.
After installation, AVG prompts for an update (so that it knows about all the viruses to that day), then it prompts to run a scan on your PC.

(http://www.ciao.co.uk/AVG_Anti_virus__Review_5602226)