I've installed ZA 5.5.114.000 (eTrust Security Suite v2.0) and vsmon.exe increase his memory... After a lot of test, I've disabled Upnp support in my router and now vsmon.exe use constantly about 13mb of memory... it works fine... but Upnp in my lan is not usable (now, i don't need it)... Have you try this way to solve the problem?
(sorry for my poor english)