Antivirus software is a must for anybody who shares files or spends hours connected to the internet. If you were unlucky enough to become infected some viruses can leave your pc in such a mess that the only solution is to reformat and you will loose anything stored on the hard drive, just imagine loosing all your holiday or family photos, letters and mp3 music files.
Thankfully there are antivirus programs to stop this from happening and FREE is the best price of all !! There are 2 that I have tried and tested.

2) Avast : Updates daily, scans in background and also checks website pages for trojans and stops them dead.