Nagra 2 was cracked, in such a way that they could generate daily keys from the main keys, this was different to the old Sky days when videocrypt wasn't cracked instead some disgruntled employee decided to hand out the master keys from which the main keys and daily/user keys are generated
Look at Sky's current encryption NDS, has been out for years and apart from brief security problems (as Horace mentions) it's soon been patched and is as secure today as it was when it first came out. Nagra3 looks as though it too will stand for a bit and probably in VM's case well into the IPTV era..