Police and prison staff remain the main targets of violent dissident factions.
Last night a senior PSNI source said continual intelligence reports pointed to that threat. And he again warned that the dissident groups only need "to get lucky once".
He was commenting after the latest bomb find in Derry - one targeting police officers.
For two days, this was an operation in which the security forces had to tread carefully.
They feared a telephoned warning that a mortar bomb had been abandoned may have been a so-called "come on" - an attempt to lure them into an ambush. But a "substantial bomb" was found.
PSNI intelligence and the Security Service MI5 have had significant successes against dissident factions in recent months, including Continuity IRA and a coalition that brought a number of republican groups under an 'IRA' umbrella.
Painstaking covert listening and watching operations have resulted in many arrests.
"There's a degree of paranoia with them that we are trying to feed," a senior PSNI source said.
But the latest bomb plot is another indication of a continuing and serious threat.
For all the successes of recent covert operations, the dissidents have not been forced into retreat.
In a recent speech, the Director General of the Security Service Andrew Parker set the threat in context - 20 attacks on police, prison officers and others last year, but most of them unsuccessful. But he warned: "The key statistic is that for every one of those attacks we and our colleagues in the police have stopped three or four others coming to fruition."
Much of that is down to intelligence operations that stop the dissidents in their tracks - surveillance that gives rise to that "paranoia" within dissident ranks.
But there is clearly is no room for complacency.