Grab Bitdefender Free. Make sure it's the Free version. That's all you need in terms of standard virus protection. You will need to create an account but it's free. You will not get spam E-mails or anything. At least I haven't and I've installed Bitdefender Free on many computers with the same E-mail and password.
Now that's just basic protection which most use. But if you want to make sure you don't get hit by a zeroday (malware that doesn't have a definition) then you also need to look into a sandbox enviroment. VooDoo Shield could fit that void or use Sandboxie for your browser. Please read about these two products before you use them so you know how to use them and what to expect. Sandboxie has a support forum. If you don't browse haphazardly, etc, then Bitdefender Free should be all you need. There's more, but it will just add cumbersomeness.