If your machine gets infected you format all because it is insecure by definition. You might even need to throw out physical machine...
If you get one it downloads ten other and you don't know which one will pass your virus scanner.
It is not fun and games anymore, silly nerds having fun are not doing it. It is actual crime and really bad guys that would kill you without blinkink an eye are doing malware.
If there is one infected file on your domain you consider whole domain compromised.