Microsoft's chief lawyer says that government snooping on its servers constitutes a threat as serious as "sophisticated malware or cyber attacks".

He also pledged to open up some of its code for peer review to reassure customers that there are no "back doors" to allow unauthorised access to informaiton.

Brad Smith, Microsoft's general counsel, said that the company is adding encryption to connections between its servers, to thwart unauthorised snooping by government agencies tapping into fibre-optic cables. That follows identical moves by Google and Yahoo to protect their internal communications against unauthorised surveillance.