I can't believe that tweaker suggested getting anti virus software from a torrent!
Torrents are about the worst thing about for giving computers viruses and to suggest getting the one thing that is meant to protect you from viruses from a torrent is ludicrous.
I would rather have either no anti virus at all or the worst possible free one installed then the best in the world if it came from a torrent!
If you de-install a security programme every year, using a removal tool, and install a new one, is there any danger of leaving bits behind that slow the computer up?