Already in use in America since 1997, the VideoGuard system was introduced to the UK by NDS in 1998 with the launch of Sky Digital, replacing the VideoCrypt system (also supplied by NDS) in use on Sky's analogue broadcasts.
Some channels on 2D are encrypted with Videoguard (a proprietary encryption method by the NDS Group) and only Sky Digiboxes with valid cards, or standard hardware with non-approved (with respect to the Sky/NDS end-user contract) "Dragon", or "T-Rex" Conditional Access Modules can decode these channels.