At the moment, I recommend Avira Free anti-virus. This will probably change in a year or two, since the last few years have seen many players in this market with many crappy products released. Bitdefender, MS security essentials, Avast, and yes, even clamwin, even though it is an open source, freely supported program.
The other issue is actually USING the AV software...most peeps install it, update it, then think it will do all the work for you. You have to take the time to setup routine FULL scans in off hours then READ the log files on the same routine.
And stated earlier..NO ROOT(administrator) ACCESS. If you let employees use your work pc's with root access then you deserve every virus/Trojan/toolbar you get!!!
MSI X58A-GD65, email@example.com, 2X-EVGA 660 GTX SC SLI, Neutron 240 GB,2.75 TB Spindle Storage,ASUS DVD-RW, 6GB Patriot, Win 7 & 8 & Ubuntu 12.10 Triple Boot, ASUS VK278 on DisplayPort.