cabbie - 11:20 pm on Feb 23, 2013 (gmt 0)
Have you checked your website thoroughly for a hack?
Checked your .htacess file or your servers configuration.
Have you checked your source of traffic?
If there is a lot of referral traffic, is that traffic bonafide?
Put up some affiliate banners and see if you make any sales from your traffic.
Put up alternative ads and see how they perform.