It's proven in old versions of Sub7 that a master key exists.
Even once I got curious about that and tried to reverse the trojan on my own with the help of SoftIce (the great debugger) and saw that there was really a master key however mobman had done too much coding to hide it...
Then someone whispered the reversing secret around and mobman had to change it or play some other trick on the next versions.
Well perhaðs I was not the first and only one who found that trick actually. Trojans are lame. But if you really need to use one, then code your own trojan...