I was playing in a game just now with somebody who was clearly a modder: http://www.bungie.net/stats/reach/gamestats.aspx?gameid=61291 2295&player=clinlab
He was on the opposing team and clearly does not have an appropriate gamer tag. They won the game within seconds and the player had full modded armor. He was also able to change the name on his gamer tag during the game. When I selected him as an avoided player it said the gamer tag of the avoided player was: HLObbies17.