I'm not sure whether this link will work. If it does it's for the ETrust server edition (still free). It uses 2 engines, the inoculateit and Vet. One can be set for real time, the other for scans, updates daily or more, and is a good freebie. It takes some time to set up, but with 2 scan engines, it'll catch almost everything. IF THE LINK WORKS.

http://etrustantivirus-east.ca.com/v7/

*edit* after loading, be sure to update since it's a year out of date. This is a server (enterprise) edition but works very well on a desktop, is relatively easy on resources, and is light years ahead of ETrust EZ, which does nothing in my opinion.