Mr Scarfo used an encryptionprogram to scramble his computer files so that when the FBI gained access to his hard disk in January 1999, it was unable to unscramble them without the password.
"Skype is a nightmare for law-enforcement agencies" because of its encryption, says David Vincenzetti, chief executive of Milan-based HackingTeam, which sells a program called Remote Control System that works on computers, smartphones and Blackberries.