Sony Pictures Entertainment has hired FireEye's Mandiant cyber-forensics unit to clean up a massive hack that knocked out its computer nearly a week ago.
The US Federal Bureau of Investigation (FBI) is also investigating the incident, said one of three people spoken to by Reuters yesterday about the incident, who were not authorised to publicly discuss efforts to deal with the attack.
Technicians are making headway in repairing damage caused by the attack and expect to have the email systems back online sometime today, said the source.
Mandiant is an incident response firm that helps victims of breaches identify the extent of attacks, clean up networks and restore systems and has handled some of the largest breaches uncovered to date, including the 2013 holiday attack on Target.
Sony executives have declined to comment on the scope of the attack, though emails have been bouncing back with messages asking senders to call employees because the system was "experiencing a disruption". Representatives of FireEye and the FBI also declined to comment.
The Los Angeles Times reported that the computer systems at the Sony subsidiary went down last Monday after displaying a red skull and the phrase 'Hacked By #GOP', which reportedly stands for Guardians of Peace.
Technology news website Re/code reported on Friday that Sony was investigating to determine whether hackers working on behalf of North Korea have launched the attack in retribution for the studio's backing of the film 'The Interview', a comedy about a CIA attempt to assassinate North Korean leader Kim Jong Un due to be released on 25 December in the US and Canada.
Pyongyang denounced the film as "undisguised sponsoring of terrorism, as well as an act of war" in a letter to UN Secretary-General Ban Ki-moon.