Some 25 years on from the Good Friday agreement many who are from nationalist communities still feel unsafe to publicly declare their work for the Police Service of Northern Ireland (PSNI).

In February, the New IRA claimed responsibility for the shooting of Detective Chief Inspector John Caldwell, who was seriously injured in the gun attack in Omagh.

The following month the terror threat was raised from substantial to severe, meaning attacks are highly likely.

"That threat comes from dissident Irish Republicans, the self-styled New IRA in particular, a conglomerate of breakaway factions still pursuing Irish unity by violent means," said Sky News senior Ireland correspondent David Blevins.

"The release of the names and ranks of an estimated 10,000 serving police officers and civilian staff plays right into the hands of those who deem officers of the crown legitimate targets."

Earlier this year, Chief Constable Simon Byrne said he receives almost daily briefings about plots to attack and kill his officers, and that the ongoing threat from dissident republicans remains a "real worry".

Luckily no home addresses were in the data published online but the response to an FOI request contained the surname, initials, rank, work location and departments for all PSNI employees.

It also revealed members of the organised crime unit, intelligence officers stationed at ports and airports, officers in the surveillance unit and almost 40 PSNI staff based at MI5's headquarters in Holywood, the Belfast Telegraph reported.

The data was potentially visible to the public for between two-and-a-half to three hours.

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Liam Kelly, chair of the Police Federation for Northern Ireland (PFNI), said a lot of officers "take exceptional and extraordinary actions" to ensure their role and identity is kept secret, including hiding their work from their families and friends.

He said for some working in the "most dangerous aspects of policing" the "veil of secrecy is their shield" and now a number of officers are feeling "particularly vulnerable" because their identities have been potentially revealed.

Mr Kelly said the force now has a responsibility to make sure they feel safe. Some officers may not be able to continue in their job or may have to move locations or from their homes.

Asked if the breach could be useful for terrorist organisations, the force's Assistant Chief Constable Chris Todd said it is of "significant concern".

He said there are no immediate security concerns, but added: "We operate in an environment at the moment where there's a severe threat to our colleagues from Northern Ireland-related terrorism and this is the last thing that anybody in the organisation wants to be hearing."

The Democratic Unionist Party's (DUP) Policing Board representative MLA Trevor Clarke described the breach as "unprecedented".

He said: "This not only jeopardises the safety of officers, but will further undermine morale within the organisation at a time when staff are holding the line amid unprecedented budget cuts."