Finnish mobile maker Nokia was blackmailed into paying hackers millions of euros, a local broadcaster has reported.

MTV - not the music channel - said hackers threatened to reveal parts of Nokia's source code for its mobile operating system.

A police spokesman said an investigation involving blackmail and Nokia was under way, but did not give more details.

Nokia has refused to comment.

"We are investigating felony blackmail, with Nokia the injured party," Det Ch Insp Tero Haapala told Reuters.

He did not go into further detail about the precise nature of the case.

However, Finnish television channel MTV said hackers had acquired encryption codes relating to Nokia's Symbian software - and had threatened to make the information public.

If they had done so, it could have made it difficult for Nokia to prevent the spread of malicious software on its smartphone devices.

'Lost track'

MTV reported that Nokia contacted Finnish police and had arranged to pay a ransom fee in a car park.

The money was picked up, the broadcaster said, but police "lost track" of the culprits.

A spokesperson for Finnish police could not be reached by the BBC on Wednesday.

Nokia - of which the handset division was recently acquired by computing giant Microsoft - now runs Windows Phone software on the majority of its devices.

Hackers demanding ransoms is a growing threat, according to security firms.

Last year, it emerged that police in Massachusetts had paid a ransom after their systems were hit with the Cryptolocker ransom virus.

Paying up is not to be encouraged, said Jon French, a senior security analyst for AppRiver.

"Paying can only further show other hackers that they have a chance of making a lot of money from these corporations," he said.

"Nokia seems to have gotten incredibly lucky that the hacker didn't release the key anyways."

The hackers must be so clever