The files were recovered in an Orange hall this week. They contained photographs, addresses, phone numbers and other details of republicans from South Armagh and Greater Belfast.
Security sources said they had been in the possession of senior members of the Orange Volunteers, a breakaway group linked to a pipe-bomb attacks on Catholic families. The RUC said that after examining the documents police were of "informing those persons considered to be at risk".
It was understood the operation could take some days but police were determined to warn everyone they believe to be under threat as quickly as possible. A number of people arrested in County Antrim after the documents seizure were still being questioned by the RUC last night. Several men have been charged in recent days in connection with the province-wide drive against loyalist dissidents.
Weapons, ammunition and pipe-bombs were seized in operations against the Orange Volunteers and another splinter group, the Red Hand Defenders. With no sign of an end to the police operation, computer equipment and another batch of documents were seized in more police swoops earlier yesterday.
An undercover team raided premises in Coagh, County Tyrone as part of the crackdown. The Coagh Community Group said 10 RUC officers kicked down the door of its premises early yesterday. The group said police carried out an extensive search before taking away the computers and documents but there were no arrests. The centre is used by Protestants and Catholics for social activities and it is understood the RUC had also been based there in the past to give advice to the public.
Peter Mandelson, Secretary of State for Northern Ireland, has sent a letter to the RUC Chief Constable, Sir Ronnie Flanagan, praising his officers for their successes in the purge against dissidents.