Along with other updates, patch 1.08 will include a fix for the damage proficiency exploit in Modern Warfare 3.
Robert Bowling has revealed that “the ‘damage’ proficiency exploit is already fixed in the next patch. We’re now tracking anyone abusing it and will ban offenders.” Bowling went on to explain, “the exploit allowed you to assign Damage proficiency to primary weapon classes that didn’t have it available. No way to do it by accident.”
On another note, Infinity Ward is ”doing some updates to the leaderboards right now, so you might notice some wonky scores or incorrect placements for a little bit.”
Title update #8, patch 1.08, will be available for players to download some time this month.
Subject: Modern Warfare 3 Patch 1.08 Will Fix “Damage Proficiency Exploit” 
Fri Jan 13, 2012 6:23 pm