By Michael Holden
LONDON (Reuters) - British police said their communications remained secure on Thursday after hackers linked to the anti-establishment group Anonymous blocked an anti-terrorism hotline and illegally recorded a security unit's officers discussing their actions.
An activist group called Team Poison jammed the hotline with repeated calls - so-called "phone bombing" - preventing those with genuine concerns from getting through in the latest attack on a high-profile institution.
Recordings of the hoax calls to the hotline, which is manned by specially trained police, and of other officers apparently from London police's Counter Terrorism Command (CTC) discussing the attack have been put on the YouTube website.
London's Metropolitan Police Service (MPS) said it had conducted an investigation and was confident its internal communication system had not been penetrated.
"We have throughout the day researched the allegation that the Anti-Terrorist Hotline had been 'hacked' and activists' claims that they were able to listen unrestricted to confidential communications," said Ailsa Beaton, director of information for the London police force.
"We are confident the MPS communication systems have not been breached and remain, as they always have been, secure. We are satisfied that any recording would have been made via the receiving handset only and not from an attack on internal systems," she added.
"The public can remain confident in the ability to communicate in confidence and that the integrity of the Anti-Terrorist Hotline remains in place."
Hackers had disrupted the Home Office (interior ministry) website on Sunday, although a spokeswoman for the department said the site itself had not been breached.
In February, Anonymous published a recording of a confidential call between FBI agents and London detectives discussing actions they were taking against hackers.
The latest recording appears to capture a handover conversation between CTC officers at the end of a shift. One said they had received about 700 hoax calls from Team Poison which had prevented any genuine callers getting through.
Other clips on YouTube featured officers speaking to one hacker, who appears to have an American accent and gives his name as Trick. He also refers to Ryan Cleary, a Briton who has been charged with phone-hacking offences.
"Other people can't get through because you are constantly putting this Team Poison stuff on," a female officer says.
After the call is ended, a number of people can be heard sniggering.
Twitter messages suggested a variety of motives for the attack on the Home Office, including government plans to boost digital surveillance powers and Britain's extradition treaty with the United States, which critics say is biased in Washington's favor.
The messages warned there would be further attacks on British government websites every Saturday.
During the recorded calls, Trick says his group is carrying out the attacks to embarrass governments and foil the police. A message on the Twitter account purportedly belonging to Team Poison said: "Free all the innocent people you've imprisoned".
(Additional reporting by Tim Castle; Editing by Myra MacDonald)