I voted other. While I don't particularly care for the people who created the viruses themselves, it's really Microsoft who should be taken to task here. They have supplied the masses with a huge honey pot, riddled with insecure access points. It screams "Attack Me!" One has to wonder how long is it going to take -- or what is it going to take -- to get Microsoft to step up and make their system secure. As long as they are getting people's money - Microsoft doesn't care.
No other plateform has these problems.
The worst thing to happen to the internet was Microsoft.