Two teenagers have been arrested over the recording of calls made to Scotland Yard's Anti-Terrorist Hotline.
The boys - aged 16 and 17 - are being held by police in the West Midlands on suspicion of offences under the Malicious Communications Act and the Computer Misuse Act.
Ailsa Beaton, Director Of Information for the Metropolitan Police said:
"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.
"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.
"The public can remain confident in the ability to communicate in confidence and that the integrity of the Anti-Terrorist Hotline remains in place."
A teenager eavesdropped on highly-sensitive police counter-terror conversations after bypassing technology from the 1980s, hackers claimed today.
The leader of an anarchist group known as Team Poison said it was "easy" to drop "a 24-hour phone bomb" on elite security officers.
Scotland Yard is understood to have been hit with more than 700 calls before an American-sounding caller, using the name Trick, told them they were being "pranked."
Detectives said "appropriate action would be taken" as a number of recordings were posted on YouTube by Team Poison.
Highly-sensitive telephone conversations on Scotland Yard's anti-terrorist hotline have been recorded by hackers.
The force said it launched an investigation today after being made aware that the phone calls might have been breached.
A force statement said: "We are aware of an issue whereby telephone conversations relating to the anti-terror hotline were recorded.
"Officers are currently looking into the matter and appropriate action will be taken."