This technique is becomming more common, with a recent study concluding that 1.3 million ads are viewed per day. 1.3 MILLION!!
Here's some more information below from the ZDNet article that I read.
New research released by Dasient indicates that based on their sample, 1.3 million malicious ads are viewed per day, with 59 percent of them representing drive-by downloads, followed by 41 percent of fake security software also known as scareware
The attack vector, known as malvertising, has been increasingly trending as a tactic of choice for numerous malicious attackers, due to the wide reach of the campaign once they manage to trick a legitimate publisher into accepting it.Thanks to Dancho Danchev for the great article.
More findings from their research:
•The probability of a user getting infected from a malvertisement is twice as likely on a weekend and the average lifetime of a malvertisement is 7.3 days
The research’s findings are also backed up by another recently released report by Google’s Security Team, stating that fake AV is accounting for 50 percent of all malware delivered via ads.