Sorry to sound like a broken record here..but:
http://www.bbc.co.uk/sport/0/athletics/23307913
Tyson Gay, US record holder and former US champion, and Osafa Powell both recently busted.
In fact, all but 2 of the top 8 fastest sprinters have been caught:
http://collegetimes.ie/2013/07/15/100m-sprint-cheats