There is no 100% effective AV system.....end of March begining of April we had an outbreak in our network (PCs on Mcafee VSE8.7, back end on Sophos). None of the systems detected the nasty....3 full days to find and upload source files to McAfee to issue an Extra.DAT to clean the infection....
I'm on KIS2011 atm, but will switch to MSE + MBAM as the price for Kaspersky products are minimum of £15-£18/3 licenses/year