Microsoft has been granted a patent for "stealthy audio watermarking," which is just a slick way of saying inaudible digital watermarks directly embedded in the audio of a file, allowing the owner to be traced. Apparently, in their version of the tech, the watermark's scattered throughout the file so it's more difficult to pull out or tweak and it's able to be compressed while remaining intact. You'd think they'd worry about actually selling music before trying to tie it down, though.