The awaited release of Halo 2 for Windows Vista has seen a slight delay due to partial nudity being present in the game. Here is Microsoft’s statement regarding the delay:

It has come to our attention that an unfortunate, obscure content error which includes partial nudity was included in our initial production of “Halo 2” for Windows Vista. As such, we have updated the initial game packaging at retailers with a label, so customers are aware before purchasing the game. Additionally, we've developed an online update which can be downloaded from www.halo2.com to remove the content. At Microsoft we take the Entertainment Software Ratings Board (ESRB) guidelines very seriously and hold ourselves to high standards, with our customers always in mind.
The partial nudity is actually not even in the game and is likely to be inaccessible to the vast majority of users; it looks like one of the game developers thought it would be funny to show his bare backside when a particular “.ASS Error” occurs using the map editor tool. Although not really a big deal, Microsoft is worried about what content gets shipped and thus delayed the release of the game to May 31st in North America.