Mohan Srivastava, a geological statistician living in Toronto, figured out a way to tell which scratch-off lottery tickets were winners, with 90% accuracy. He told the Ontario lottery authorities, and they took that particular game off the market. But most scratch-off games are flawed in similar ways. Here's a fascinating article from Wired on how he did it, and other flaws in the lottery systems.
[Thanks for the pointer, Jan.]