If u want a free edition try also Microsoft Security Essentials, but for a better security u can try first and buy after some pay AV. G Data Internet Security, Kaspersky I. S.,Nod 32, are very good products.And Norton I.S.
quick heal antivirus is not supporting for windows 7 but i need to support that antivirus
Buy gdata it is avast and bitdefender antiviruses under the same program!
AVG Free it's one of the best free ones you can find.