Law enforcement officers are unable to monitor calls made over the Skype networking meaning that criminals and terrorists could have a free hand, according to a leading German police officer.

Experts have been unable to decrypt Skype phone calls said Joerg Ziercke, president of Germany's Federal Police Office (BKA). "The encryption with Skype telephone software ... creates grave difficulties for us," said Ziercke. "We can't decipher it. That's why we're talking about source telecommunication surveillance - that is, getting to the source before encryption or after it's been decrypted."

The authorities are not going so far as to make Skype divulge its encryption, an approach that has caused much controversy in the US, with both the Clipper Chip in the 90s and the current row over RNG technology He said that there had been no discussions with Skype on the matter as he did not think they would help the situation.

Ziercke favoured a different tack: he said there was a need for police to be able to mount hard-drive searches of suspected criminals as he said there was evidence that they would leave incriminating data on PCs rather than run the risk of mailing it.

Only last week, a researcher claimed that companies using the SIP protocol would leave themselves vulnerable to hackers. It seems that Skype's proprietary protocol has an unwelcome consequence for law enforcement.