An anonymous reader writes "Microsoft has just received a little-known patent for a "Stealthy audio watermarking," which is seemingly uncrackable, since it uses spread-spectrum technology to hide its traces within music files. As the patent's abstract explains it: "The watermark identifies the content producer, providing a signature that is embedded in the audio signal and cannot be removed. The watermark is designed to survive all typical kinds of processing and malicious attacks." True, watermarking is not the same as file encrpyption. However, an end-to-end music system could use watermarking to verify ownership. Does this mean it might be time to revise the DRM scorecard?"