These letter bombs are not big explosive devices capable of causing widespread damage.
The threat they pose is very specific. It is to anyone who might open one of the packages.
Up to this point that hasn't happened.
In all cases, someone has become suspicious, raised the alarm and the Army called.
The devices are in jiffy bags or padded envelopes and, in at least one case, wires were visible.
For the dissident IRA this is low-risk activity – low-risk for them.
It does not involve the type of planning and numbers that would be required for transporting a bomb or carrying out a gun attack.
But the dissidents will know there are headlines in the letter bombs.
Just writing the names of the chief constable and the Secretary of State onto the packages means everyone has again been reminded of a continuing threat.
But the dissidents will know something else.
Matt Baggott and Theresa Villiers were never going to open the packages addressed to them.
So, had they been opened, it was somebody else who was going to be hurt. What will be particularly concerning is that one of these packages got as far as Stormont Castle.
There have now been four incidents. Two devices have been intercepted and worryingly two have been delivered.
The unanswered question is how many more could be out there in the postal system and whose name will be on the next package?
For months the dissidents couldn't move, couldn't breathe.
The watching and listening of the intelligence services and police meant many planned attacks were interrupted.
So the dissidents paused and adjusted tactics – using hoax alerts to disrupt travel and now these letter bombs.
It's a reminder of a continuing threat and that the many IRA factions are still out there.