There is no need to pay a monthly fee to an antivirus editor to protect your PC efficiently. Avast antivirus is a totally free software (for a non-commercial use) and offers all that is necessary to parry virus, worms and trojans. It offers antivirus scan, firewall, intrusions detection, P2P protection... In order to use this software, you'll only have to register freely online with a valid email address. You'll get a serial number valid for 15 months, after which you'll be able to renew it in the same way. Don't worry, they don't seem to send any newsletter or spam to these emails. This version 4 of Avast Antivirus is fully compatible with Windows Vista RC1.