How did you get infected: The possibilities are great. Most recently we observed agressive email spam campaigns to infect users with FakeAlert and subcomponent Antivirus XP 2008. One notable campaign sent fake CNN news alerts. The alerts were identical to actual alerts sent by CNN and MSN. When the user clicked a link to a "news story" they were brought to page that looked identical to a CNN page and prompted to download a video codec to watch the news alert. Upon doing this, the user became infected. Read more at:
http://ca.com/securityadvisor/pest/pest.aspx?id=453137615