"... I start looking at the tic-tac-toe game, and I begin to wonder how they make these things,” Srivastava says. “The tickets are clearly mass-produced, which means there must be some computer program that lays down the numbers. Of course, it would be really nice if the computer could just spit out random digits. But that’s not possible, since the lottery corporation needs to control the number of winning tickets. The game can’t be truly random. Instead, it has to generate the illusion of randomness while actually being carefully determined.”
He discovered that the numbers on the card before scratching provided information about the numbers underneath the latex. Specifically, he found that "singletons" - numbers present only once on a card - were likely to indicate the location of a successful scratch. After cracking the code, he calculated that he could win about $600/day if he spent full-time buying and scratching cards. Instead, he took his information to the Ontario Lottery and Gaming Corporation.
A sample card is shown at left. Details of his logic and calculations are explained at the Wired link.