How are so many people getting infected with the Antivirus 2008 trojan?

Being a computer professional I have been inundated with calls from clients who have contracted the Antivirus 2008 trojan. Trying to ask them how they believed to have caught it is like asking the paparazzi why are they so infatuated with Brittany Spears.... they just don't know. So I am going to leave it to you capable individuals in answering my questions as to how you or someone you know contracted that pesky Antivirus 2008 trojan?