Criminals in Italy are increasingly making phone calls over the internet in order to avoid getting caught through mobile phone intercepts, police say.
Officers in Milan say organised crime, arms and drugs traffickers, and prostitution rings are turning to Skype in order to frustrate investigators.
The police say Skype s encryption system is a secret which the company refuses to share with the authorities.
Investigators have become increasingly reliant on wiretaps in recent years.
Customs and tax police in Milan have sounded the alarm.
They overheard a suspected cocaine trafficker telling an accomplice to switch to Skype in order to get details of a 2kg 4.4lb drug consignment.
Use of wiretaps by prosecutors in Italy has grown exponentially in recent years.
Investigators say intercepts of telephone calls have become an essential tool of the police, who spend millions of dollars each year tracking down crime through wiretaps of landlines and mobile phones.
But the law may be about to change.
Prime Minister Silvio Berlusconi s right-wing government has drawn up a bill which would restrict police wiretaps to only the most serious crimes.
Much crime reporting in the Italian media is based on leaks of wiretaps and leading politicians, including Mr Berlusconi himself, have found to their embarrassment that details of their private telephone conversations have sometimes been leaked to newspapers.
Under the new law reporting of details of criminal investigations obtained through wiretaps would become illegal until a final verdict has been delivered.
Given the extreme slowness of Italian justice, this would mean that details of cases now before the courts might be reported by the press only in 15 years time.
Not only have Italian journalists been protesting at the new draft bill, but a heated debate is also going on about it within the country s highest body for the administration of justice - the supreme council of the magistrature, composed of the country s top judges.