A 50-year-old man has been arrested in Derry as part of the investigation into a data breach at the PSNI.
Last week, the PSNI revealed a document had mistakenly been shared online, which included the names of about 10,000 officers and staff.
Details released included the surname and first initial of every employee, their rank or grade, where they are based and the unit they work in.
Following a search operation in the Dungiven area this morning, a man was arrested under the Terrorism Act and is being questioned at Musgrave Serious Crime Suite.
PSNI Detective Chief Superintendent Andy Hill said: "We continue to work toward establishing those who possess information relating to last week's data breach, and will taken action to ensure that any criminality identified is dealt with robustly to keep communities, and our officers and staff who serve them, safe".
A second man, who was arrested earlier this week in connection with the data breach, was released on bail yesterday.
The 39-year-old man had been detained following a search in Lurgan, Co Armagh on Wednesday.
He had been questioned on suspicion of collection of information likely to be of use to terrorists.
Earlier this week PSNI Chief Constable Simon Byrne said he believed the information was in the hands of dissident republicans.
It followed the posting of documents from the leak on a wall near a Sinn Féin office in Belfast.
Many officers have expressed concern for their safety in Northern Ireland, where police are under threat from terrorists - with the current level of threat assessed as severe, meaning an attack is highly likely.
