I have Internet Security, but i since i previously used Norton, and that ye, eats resources, i feel it now much more light, and tough i may turn it off(kaspersky) and don't notice anything i belive there are even more lighter anti virus. Guess i'm just lucky or stupid for not noticing anything :p
And it is free! :)
best antivirus programms overall but are expensive and needs a lot of system requirements: kaspersky & avg