Hackers have recorded calls between staff manning Britain's anti-terrorist hotline, Scotland Yard revealed on Thursday, in the second security breach involving the force in recent months.
Hoaxers also telephoned the hotline, a confidential service allowing people to report suspicious behaviour, and recorded the conversations they had.
The London police force said it had launched an investigation into the breach and urged members of the public to continue using the service.
"We are aware of an issue whereby hoaxers have made calls to the anti-terrorist hotline and have made recordings of their conversations with anti-terrorist hotline staff," it said in a statement.
"In addition, recordings have been made of conversations between Metropolitan Police Service (MPS) anti-terrorist hotline staff."
It said the investigation was being led by Scotland Yard's cyber crime unit, adding: "The anti-terrorist hotline remains operational and we continue to urge members of the public to report any suspicious activity to the police.
"Public reporting is an important part of the fight against terrorism and any attempt to disrupt this service will be investigated thoroughly."
In February, hacker group Anonymous released a recording of a conference call between Scotland Yard and FBI officials discussing operations against the collective.
The British force said at the time that it believed that none of its systems had been hacked, while the US law enforcement agency said it had launched a criminal investigation into the breach.
In an advertising campaign entitled "It's probably nothing, but...", Scotland Yard promotes its anti-terrorist hotline as a confidential way for people to report suspicious behaviour.
"We know you may have concerns about speaking to the police -- possibly because your friends or family may find out. But all information passed to the police is treated in the strictest of confidence," it says.
Britain's intelligence services currently judge the threat level to the country from international terrorism to be "substantial", the third of five levels meaning an attack is a strong possibility.
© 2012 AFP