The force declared a critical incident last week after data on all 10,000 officers and staff was accidentally disclosed online.

Detectives carried out a search in Lurgan, County Armagh, on Wednesday and arrested a 39-year-old man.

Detective Chief Superintendent Andy Hill said the force was "working tirelessly to address the risk posed to officers and staff" and the arrest was "one piece of a large-scale operation".

"We will continue in our efforts to disrupt criminal activity associated with this Freedom of Information (FOI) data breach and to keep communities, and our officers and staff who serve them, safe," he said.

Sky's senior Ireland correspondent, David Blevins, said police were not investigating the breach itself, but that the arrest came after the leaked information had been widely circulated online.

The leaked names appeared online for two hours after the force responded to an FOI request from a website that wanted to know how many officers were serving in each rank.

However, it appears someone inadvertently attached a spreadsheet to the reply that also included their names.

The data is thought to now be in possession of dissident republicans.

A redacted version of the document was earlier this week posted on a wall facing a Sinn Fein office in Belfast in a "sinister" attempt to intimidate one of its politicians.

"There are serious concerns among police officers and staff - the police federation here is calling for maximum vigilance," said Blevins.

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The FOI data leak was followed by disclosure of a second breach in July relating to stolen documents and a laptop.

Names of around 200 serving officers and staff are believed to have been on a spreadsheet on the laptop, which was taken from a private vehicle in Newtownabbey, near Belfast.

A police issue laptop and radio are also thought to have been stolen.

Head of the Catholic Church Archbishop Eamon Martin met PSNI Chief Constable Simon Byrne today and said he has spent time with Catholic officers and their families since the data breach.

"I am in no doubt but that the future of peace and prosperity across the island of Ireland will depend upon respect and support for policing," he said.

"Today I assured the Chief Constable that all members of the PSNI, and their families, are in my prayers at this time.