if your windows original setup microsoft security if not you can download free antivirus ( avira ) from : avira.com
Try avast antivirus. The best thing I like about avast is that it directly delete the virus without informing the users, which could harm your pc.
Avast is the best antivirus. It is used by the national security agency i think. And they currently offer a free version which isn't any worse than a premium one.