Almost four years ago, in an interview with this newspaper, the leadership of Oglaigh na hEireann boasted: "Nothing is beyond our reach."
The comment came during an interview I conducted after an elaborate series of precautions were put in place by the people I was going to speak with.
Under cover of darkness, on a winter's evening, I was picked up outside Clonard Monastery and driven to a house somewhere in west Belfast.
Inside, at the top of the stairs, I was searched and then shown into a bedroom where three men were waiting to speak to me.
Throughout the meeting one of them held some type of electronic scanning device, constantly checking the colour of the lights on its display.
This is the cat-and-mouse world in which the dissidents operate.
They are always aware of the possibility of covert listening and surveillance. They are always suspicious that their conversations are being heard and recorded.
For the security forces, intelligence is critical in the prevention of murder and destruction, and the security service MI5 and the PSNI have a range of devices to help them get it. Their covert eavesdropping methods allow analysts to get inside the thinking and doing of the dissidents.
Yesterday, I saw a leader of the Oglaigh na hEireann faction walking and talking on the Falls Road. He would regard it as safer to do his talking outside and on the move, rather than meet on the same street corner or in the same house or office.
For the dissidents the challenge is to operate outside the listening circle, while the job for MI5 and police intelligence is to ensure that doesn't happen. They achieve this through the gadgetry and methods that have become part and parcel of the intelligence war.
Just look at how many dissident operations have been interrupted, how many arrests have been made, and how many bombs have failed to explode or only partially detonate. These are not chance happenings but, often, the end product of intelligence gathered.
We know that explosives have been removed from bombs, that weapons have been bugged, that there are those inside the dissident organisations – so-called covert human intelligence sources – who are also working for the forces of law and order.
But there is no such thing as 100% intelligence. In this murky world, the pendulum swings back and forth – success for the police then a setback from the dissidents.
There are times when groups such as Oglaigh na hEireann are afraid to move, afraid to talk. They will always be asking themselves: who might be watching, who might be listening and who among them might be talking?
What was that conversation I witnessed on the Falls Road about yesterday? Was it about trying to avoid those who might be listening?
The dissidents must know that much of their talking and planning is within the earshot of MI5 and police intelligence.
It is why so much fails.