Microsoft is recovering from a bit of an embarrassment recently, as they have now admitted that a botched update for the Xbox 360 is what caused some people to completely lose audio on their systems. The update included a change to HDCP, which has been identified as the source of the problem.
Some workarounds included using analog audio temporarily, which was a workable solution for those who had devices capable of taking analog input. A more crude workaround was to pull the hard drive from the system, preventing the updated software from loading, which is certainly an unacceptable solution to a problem caused by an update to HDCP. Microsoft hasn't mentioned anything about how many users were affected only that it was a "very small number."