A 39-year-old man has been arrested by PSNI detectives investigating criminality linked to last week's data breach.
The man was arrested on suspicion of collecting information likely to be useful to terrorists.
He was detained after a search was carried out in Lurgan, Co Armagh and is being questioned at Musgrave Serious Crime Suite.
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.
PSNI Chief Constable Simon Byrne said on Monday he believes the information is in the hands of dissident republicans, who are opposed to the peace process.
Detective Chief Superintendent Andy Hill said: "We are working tirelessly to address the risk posed to officers and staff.
"Today's search operation, and subsequent arrest, is just one piece of a largescale operation.
"We will continue in our efforts to disrupt criminal activity associated with this freedom of information data breach and to keep communities, and our officers and staff who serve them, safe."
