The terror threat facing prison officers in Northern Ireland remains severe, MLAs have been told.
Sue McAllister, the director general of the prison service in Northern Ireland, said dissident republicans, who shot a prison guard three years ago, were still intent on murder.
She told members of Stormont's justice committee: "It is severe. It has been severe for some time and we continue to take it very seriously."
David Black, a 52-year-old father of two was gunned down on the M1 motorway in Co Armagh in November 2012.
He was the 31st member of the prison service to be killed in Northern Ireland.
Security measures include warning staff about the dangers of using social media as a means of communication.
However, Ms McAllister acknowledged it would be challenging for new young recruits.
She said: "This new generation of CPOs (custody prison officers) coming in would use social media as a way of communicating."
DUP MLA Edwin Poots, who met Mr Black's widow in the summer, said it was imperative to avoid another murder.
He said: "The pain and anguish is still there. We must do everything we can to ensure that kind of incident does not happen again.
"We have to do everything we can to avoid another family being left in that circumstance."
Mr Poots also called for Prison Service bosses to closely monitor social media after an officer was threatened online.