The Blu-ray movie catalogue has effectively been on hold this Spring, as both Fox and MGM have declined to issue software in the format, following breaches in its AACS copy protection system. But releases could soon resume as another level of DRM is ready for introduction. BD Plus effectively places a virtual playback machine within the local player which is able to diagnose if a machine has been either modified or requested to play illegal content. BD Plus works alongside and in conjunction with AACS. The technology is not available for HD DVD discs.