avast! is a package of applications that aim to protect your computer from a possible virus infection or other malware threat. If you use it correctly, and in combination with other programs such as data backup utilities, it will significantly reduce the risk of your computer being attacked or infected by a virus, and thus the risk of losing important or private data.

You have to register for free license after installation. it's free.

http://www.avast.com/en-us/registration-free-antivirus.php