Microsoft contractors are listening to Skype users' sensitive personal conversations in order to operate its AI-powered translation service.

Human workers listened in audio recordings including people talking with their loved ones, discussing relationship issues and talking about personal problems, according to clips leaked to Vice News..

One anonymous contractor also claimed that humans had listened to "phone sex" and pornographic search queries from Microsoft's Cortana virtual assistant.

A spokeswoman for the company said that it always gets permission for examining users' voice data and that users were protected by non-disclosure agreements signed by contractors and by the scrubbing of "identifying" data from voice clips.

But Skype's translation FAQ and Microsoft's privacy policy only say that conversations will be "analysed" and "verified", without mentioning that a human being will listen to them.

It is only the latest report of advanced AI systems turning out to rely on third-party human contractors manually reviewing some users' private communications without widespread public knowledge.