That is taken care of by the system updates, as already stated. Remember it's function is to scan documents and media for malware that may be passed onto Windoze users by email or file sharing, not to find malware that will attack Mac OS X (same if using AV software in Linux). And there's a LOT of anti-virus software in the App Store, but I wouldn't recommend any of it except for ClamXav. To be clear, Apple does not endorse any anti-virus software. There is a big difference between approval of software for inclusion in the App Store and endorsement by Apple. There IS antivirus scan software approved by Apple (Assuming that if it's in the App Store for purchase using Apple-ID, then de facto it's approved)
