Microsoft contractors in China reportedly listened to calls made on Skype and digital assistant Cortana as they reviewed thousands of audio recordings from Skype and Cortana without cybersecurity protection.

A Guardian report on Friday quoted an unidentified former Microsoft contractor as saying that he reviewed thousands of audio recordings from Skype and Cortana on his personal laptop from his home in Beijing over a two-year period.

The contractor said that he heard "all kinds of unusual conversations" while performing the transcription.

"It sounds a bit crazy now, after educating myself on computer security, that they gave me the URL, username and password sent over email," he was quoted as saying.

Microsoft said in a statement given to CNET that calls are now transcribed in "secure facilities in a small number of countries.

Microsoft has also made changes, including moving its review program to "secure facilities," none of which are in China.

"This past summer we carefully reviewed both the process we use and the communications with customers," said a Microsoft spokesperson. 

"As a result we updated our privacy statement to be even more clear about this work, and since then we've significantly enhanced the process including by moving these reviews to secure facilities in a small number of countries".

Microsoft in August last year admitted that third-party contractors listen to voice conversations on Skype and virtual assistant Cortana.

The revelation came after Motherboard found contractors were listening to audio from both Skype and Cortana, including sensitive and personal conversations of Microsoft customers.

Microsoft's human review contractors were paid between $12 and $14 an hour for the job, and transcribe up to 200 audio clips every hour.

Apple, Google and Amazon recently suspended human review of user audio recordings after reports said the companies used third-party contractors to listen to users' voice recordings.

While Apple suspended the programme that let its virtual assistant Siri listen to users' recordings for "quality control", Google stopped listening and transcribing Google Assistant recordings in Europe.