At home I run MS Security Essentials and do the occasional scan every month or 2 with
Malwarebytes. both are free
On the servers at our office, in addition to a physical firewall, we run Kapersky Endpoint Security 8 (not so free but works well and is light on resources)
I used to use Symantec Endpoint Small Business but that missed a pretty nasty virus and was a resource hog.
1998 328ic - Sold