Prisoner officers here remain at severe risk of terrorism, MLAs were told yesterday.
Sue McAllister, director general of the Northern Ireland Prison Service, said dissident republicans were intent on murder.
She told members of Stormont's justice committee: "[The risk] is severe.
"It has been for some time, and we take it very seriously."
Security measures including warning staff about the dangers of social media have been taken, but Ms McAllister admitted they could be challenging for new recruits.
She said: "This new generation of custody prison officers coming in would use social media as a way of communicating."
Recalling murdered prison officer David Black, DUP MLA Edwin Poots said it was crucial to avoid another killing.
He added: "The pain is still there.
"We must do everything we can to ensure that kind of incident does not happen again."
Mr Poots also urged Prison Service bosses to closely monitor social media after an officer was threatened online.
His comments came as the governor of Maghaberry insisted that Northern Ireland's only high-security jail was not "broken".
Phil Wragg said that "good progress" had been made on improving a facility recently described in the Assembly as "not fit for purpose".
He told how mandatory drug testing had been introduced and added: "We are hot on testing for drugs. We want to know exactly what the level of drug non-compliance is."
Mr Wragg, whose comments were made during a briefing for MLAs on the justice scrutiny committee at Parliament Buildings, also spoke of the difficulties of running such a prison.
"The establishment is complex," he said. "It has to deal with different types of prisoner under one roof without the ability to move people who provide us with a level of concern."
It was also revealed that a new staff canteen where inmates prepare the meals had been widely welcomed by officers.
Mr Wragg said: "It is such a resounding success that we are having to expand the facility because we cannot fit the number of people that want to use it.
"That provides an environment for staff to have good-quality food at a good-quality price.
"The important thing is there are prisoners doing the catering. There are prisoners who are earning a qualification by working."