Contrary to the previous answer Sky do NOT use Nagravision for their Conditional Access and never have done. Sky use VideoGuard from NDS (a News Corp Company).
Not only has the current version of VideoGuard not been hacked, Sky recently closed a loophole that enabled Sky cards to be used in non-Sky Conditional Access Modules. Therefore the current )August 2010) status of Sky Conditional Access is that in order to receive Sky subscription channels you need a real Sky box and a Sky Viewing card and that is likely to stay the case.
As to Nagravision (used by Virgin Cable) when the Virgin roll-out of Nagravision3 is complete, all those dogiboxes will stop working because it too has not been hacked.
T
July 2010