I'd like to know how MSE is terrible? Low memory footprint, good detection... I fail to see the problem.
ITS NOT MADE BY IBM LOLOLOLOLOLOLOLOL!!!!!!!!!!!111111111111111
Seriously though, a neighbour's computer had a dodgy hard drive which was rendering Windows inoperable (after about 6 boot cycles, Windows would refuse to boot, and would need to be reinstalled) so I decided to back up their data pending them buying a new system. They have three teenage sons with a penchant for limewire, and a bad taste in porn, so I updated and ran AVG before packing up the stuff to my disk. It picked up some stuff so I thought it was grand.
At the time, I think was running a cracked and old copy of NOD32 on my computer, and a scan picked up loads of stuff in the backup folder that the latest AVG with the latest definitions missed. Some time passed by (I told them to wait for Windows 7 to come out before getting a new system, which meant I had this stuff lying around for about a month and a half) and I had switched to Avira because my old NOD32 wouldn't update any more, and lo and behold it found things that the old NOD32 hadn't and that AVG didn't.
By the time they got their computer, I had changed to MSE (Avira had annoying pop-ups, and there was problems with their update server around the time I used it), and yes, MSE did find even more ****e still.
Other reasons why AVG sucks - it has lots of annoying pop ups and dialogs, it's big and clunky, and I've seen the updates screw up too many times. It also only handles viruses. MSE works quietly in the background and doesn't waste resources, and takes spyware on too.
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Of course, the best anti-virus is to get a Mac.