From AVAST Software:
Avast Free Antivirus for Mac offers three shields,on-demand scanning and WebRep clients which are automatically (optionally) installed to Safari, Chrome and Firefox browsers. Our Web Shield and Mail Shield combine to check the vast majority of incoming data from the Internet, while File Shield scans all programs stored and executed from your hard drive. Everything is packed in a brand new GUI.
Non cumbersome or "system slowing" Interactive pop-ups show it's "on the job"
Unfortunately, we all need some kind of AV to protect our systems these days and this particular product; I have found better than Norton in that Norton crippled my system interface speed with the web... this one is flawless.