I would suggest looking at Vipre. It runs on all versions of windows including WHS.
If look around you can find good deals on multi user versions.
Came accrossed it a number of years ago when Norton blew me out of the water on a update. Let alone ate up system resources.
Would not say perfect but does the job at decent price and little if any impact on system performance.
Vizio P75-C1 | OPPO UDP-203 | Samsung UBD-K8500
Denon AVR-x5200w | Nvidia Shield Android TV | C =Axiom VP150 |FL/FR =Axiom M60 |SL/SR =Axiom QS4 |TFL/TFR =Bose 161 | TRL/TRR =Bose 161 |Sub =Reaction Audio S-15 500W SEALED SUBWOOFER