Microsoft has begun punishing Xbox Live users who've been beefing up their gamerscores illegally.
As explained by Major Nelson, anyone caught mucking about will have their score reset to zero. They will be unable to regain any previously earned achievements, though they will be allowed to earn new ones fairly and squarely.
Worst of all, offenders will placed in stocks on the Xbox Live village green so others can throw virtual rotten tomatoes at them. Or more specifically, they will have their gamercards marked for all to see. As the example on flickr shows, that means the words "I'm a dirty cheat" will be stamped across the image space.
For more about the new system, including how to grass people up and why there's no appeals process, visit Xbox.com