The head of Sony has condemned the recent hacking of the company's movie division as "one of the most vicious and malicious cyber attacks in recent history" and praised staff for working "tirelessly" to release controversial comedy The Interview.

The hack attack on Sony Pictures has dominated headlines in recent weeks after numerous private emails hit the web, and executives axed the cinema release of Seth Rogen's latest film following a threat to U.S. theatres.

They later offered the film up online, scoring the company's biggest ever Internet hit, and several cinemas have since shown the movie.

Kazuo Hirai, President and Ceo of Sony Corporation, has now spoken out about the controversy during an appearance at the 2015 Consumer Electronics Show in Las Vegas ahead of his keynote speech there, and praised his workers for standing up for free speech.

He told reporters, "Both Sony, former employees and current employees were the victim of one of the most vicious and malicious cyber attacks in recent history... I have to say that I'm very proud of all the employees, and certainly the partners who stood up against the extortionist efforts of criminals, and worked tirelessly, sometimes for days on end to bring you The Interview... I have to say that freedom of speech, freedom of expression, freedom of association - those are very important lifelines for Sony and our entertainment business".

The hack attack has been blamed on a group linked to North Korea who are opposed to the depiction of the country's leader, Kim Jong-un, in the film.