Two youths have been arrested over the recordings of calls made to Scotland Yard's Anti-Terrorist Hotline, police said.
The boys, aged 16 and 17, were held at an address in the West Midlands by detectives from the Police Central e-Crime Unit.
They were arrested on suspicion of offences under the Malicious Communications Act and the Computer Misuse Act.
A Scotland Yard spokesman said the pair were in custody in the West Midlands.
The force said it launched an investigation after being made aware that highly sensitive phone calls might have been breached.
The Met said it was aware hoaxers had made calls to the hotline and made recordings of their conversations with anti-terrorist hotline staff.
The investigation is being led by the Police Central e-Crime Unit (PCeU).
An earlier statement said: "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."