> Officers are said to have prevented people being murdered after covertly monitoring planned attacks and threats to life on the encrypted service.

Now they can't do that any more. It's a dilemma that British intelligence faced a lot during the world wars: if they acted on information gleaned from secret channel it would reveal to the enemy that the channel was compromised. Makes me wonder how long they were monitoring and possibly letting crime take place before deciding that now was the time to strike.