New legislation is needed to give police greater powers to investigate online activity by terrorists such as dissident republicans, the head of Northern Ireland's specialist anti-terror unit has insisted.
Detective Superintendent Kevin Geddes said technology had overtaken current laws governing what data officers could and could not access to combat extremism.
The officer, who leads the PSNI's Terrorism Investigation Unit (TIU), expressed fears of "going dark" on the online contacts between potential dissident republicans.
"Going dark is really when we lose the ability to see what's happening communications-wise, and that's a real challenge," he said.
"Technology has overtaken the legislation we have, which prevents us from capturing how people communicate."
The issue of beefing up legislation is extremely politically divisive. Supporters of the move stress the need to make compromises with individual privacy to keep people safe, while opponents characterise it as a snoopers' charter.
The Government introduced emergency legislation last year to ensure internet and phone companies retained their customers' personal communications data.
But the law stopped short of including internet browsing histories in the face of Liberal Democratic opposition.
The emergency legislation will expire in 2016. Parliament is also considering law changes that would give police greater powers to access IP (internet protocol) addresses to identify specific devices using the net.
The senior detective acknowledged the issue was not straightforward and said there was a need for a public debate.
"The balance is around privacy because the more you open the legislation potentially the less privacy people have and that's always going to be the debate," he said.
"So anything that would be done would have to be with oversight and the proper legislative process. New legislation would be really, really useful."