Which is the lightest Antivirus?

Update 2017:

The lightest antivirus is Windows Defender, preinstalled in every Windows version after 8, like Windows 8.1, Windows 10, and so on…

If you have a new PC, with Windows 10, you don’t have to install another antivirus, it’s already integrated and it’s good

Which Antivirus uses less memory?

Raymond.cc tried TWENTYFIVE of them, and saw which uses less memory: Avast!

Watching the ranking, you can see that, unbelievably, Norton, known to being very heavy (the latest I tried it’s version 2003), has got much better, arriving in fourth position, even scoring better than NOD32, known to being very light.

Moreover it looks like Norton now sells for just 12$?? Wasn’t it around $50 / year??