Dissident republicans in Ireland claim to have police information leaked online.
Simon Byrne, Chief Constable of the Police Service Northern Ireland (PSNI) said the details had been gleaned from WhatsApp.
The PSNI names were published following a simple Freedom of Information request seeking the number of officers across the force.
However, buried in the data was detailed information about all the men and women serving.
Up to 40 officers at MI5’s HQ in County Down are said to be among the names published.
Moves under way to ensure their protection.
Mr Byrne said:
“I am deeply sorry about an industrial scale breach of data.
“An early worst-case scenario that we have been dealing with is that third parties would attempt to get this data to intimidate, corrupt or indeed cause harm to our officers and staff.
“We are now aware that dissident republicans claim to be in possession of this information circulating on WhatsApp.
“As we speak, we are advising officers and staff about how to deal with that and any further risk that they face.”
He added the force had not yet been able to verify the substance of the claim.
The PSNI declared a “critical incident” on Wednesday after a junior staff member published the data of all 9,276 serving officers and civilian employees, including dozens of staff who work with MI5, online.