Highly-sensitive telephone conversations on Scotland Yard's anti-terrorist hotline have been recorded by hackers.
The force said it launched an investigation 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."
The announcement from the force came as a recording said to be a "prank call" to MI6 was uploaded on YouTube, attributed to the "hacktivist" group TeaMp0isoN. The group were said to have compromised a server from Malaysia to record conversations before Trick, the leader of the group, allegedly called MI6 offices in London.
Group leader Trick emailed the Press Association: "The phone denial of service was done via a custom script for Asterisk which was installed on an overseas server.
"The conversation was tapped into via a private phreaking method, their phone system is old and we found a way to get in via basic but private phreaking technique."
In response to the Scotland Yard statement, @_TeaMp0isoN tweeted: "OH REALLY NOW."
When asked whether he found it simple to overcome MI6 security, Trick emailed: "Yes it was easy :)"
Trick is reportedly a teenage hacker who launched the group in 2010. The group has been linked to alleged hacking attempts on Facebook and a personal email account linked to a former staff member of Tony Blair's.