The word Nagravision applies to both a company with that name, and a set of conditional access systems for cable and satellite teleivison services. Nagravision encryption schemes are used by digital (and analog) providers around the world for conditional access purposes. A decryption unit is provided in the receiver either in the form of a physical conditional access module, or an emulator.
The original Nagravision system (for DTV) was compromised in 1999 but is still widely used. Decryption keys for specific providers often leak and are distributed over the Internet, but many providers fight off TV pirates by changing keys many times throughout a single day.
A version of the conditional access system known as Nagravision Aladin was compromised in 2005, leading to a cat and mouse battle between providers and satellite TV pirates. While software updates tackled the security issues, card hackers have been able to stay one step ahead of the system and continue their activities. The next version of Nagravision, Nagravision 3 (Nagra3) however, has not yet been compromised and as such, is dreaded among many.