You CAN have your console banned for having a 12v fan mod. A very trusted user of www.360patches.com got told directly from MS reps that his fan was modded on his 360 and that it violates the TOA. Any modification of hardware does indeed violate the TOA, so legally they reserve the right to ban users from live for that reason. Petty yes, but justified. A fan mod would be reasonably easy to detect, as voltage metering is something standard in all bios for the past 10 or so years.