Leading members of the computer hacking group LulzSec have reportedly been arrested in the US.
Irish police say they are also holding a man in connection with the investigation.
Court documents in New York are said to show that the group’s suspected leader, Hector Xavier Monsegur who is nicknamed Sabu, was charged last year with conspiracy in computer hacking and had pleaded guilty.
There are reports that he had been cooperating with police for a while.
He is said to have been an influential member of three hacking organisations, involved in high profile attacks on major firms including online payment companies.
Court papers say Sabu formed LulzSec last May, and operated by identifying weaknesses in potential victims’ computer systems.
LulzSec is a spin-off of the loosely organised activist group Anonymous.
Some alleged associates of the collective are already facing charges in other countries such as Britain.