Microsoft is making good on a promise it made last October to make "bad things happen" to anyone caught tampering with their Gamerscore or Achievements, and the plan includes a bit of public humiliation.
The slap from Microsoft starts by resetting the offender's Gamerscore to zero, and rendering them unable to re-earn any previously obtained Achievements. So no replays of King Kong or Gun for a quick 1000 point boost.
An appropriate punishment for the crime, but just to make sure everyone knows why your Gamerscore is suddenly so low, your GamerTag will also clearly label you as a 'dirty cheater'. (Apologies that this representative sample of a cheater's GamerTag is, ironically, not clear at all.)
Smacking down people who are unfairly tweaking their Gamerscores is all well and good, so long as only guilty people get punished. Microsoft says it uses "specific and automated" criteria to determine who's fudging the numbers, and says that anyone earning Achievements the old-fashioned way will be completely unaffected.
Microsoft is also using a very specific definition for cheating, only targeting those players who "gain achievements through avoiding game play and the use of external tools" and will only wipe the Gamerscores of players who meet their 100% of their "cheater" criteria.
There's no way to appeal a Gamerscore correction or to remove the "cheater" label, so here's hoping that criteria is extensive and leaves no room for reasonable doubt.
Source: W.I.R.E.D.