Those wishing to look at various types of antivirus software (and trojan scanners and firewalls) should look at:
http://www.wilders.org
where independant tests are performed on a wide range of programs.
There is no doubt which is the best AV program around in my opinion: NOD32.
It has real time scanning for emails, signature scanning and heuristic scanning and is blisteringly fast. You can get a trial version from
http://www.nod32.com and the support forum is at the Becky Users Forums at:
http://www.morelerbe.com/cgi-bin/ubb-cgi/ultimatebb.cgi