It appears the Federal Bureau of Investigation has made some progress on the Sony Pictures hacking case, after a week of downtime at the studio.

Reuters reports the FBI has sent out a warning to U.S. businesses, claiming hackers used malicious malware software to attack Sony Pictures, and this could be used again to other companies.

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The malware is capable of overriding all hard drives on a company's system, making it inoperable. The hackers have full control over the system and are capable of controling the boot sequence for every connected machine, allowing them to display the same message.

Removing the malware is a costly ordeal, and the FBI claims it might be "impossible" to recover the data. Recovering hard drives would be the optimal solution, but these would need to be outside of the company's system to not get infected.

The FBI has not given any names for the potential attackers, but this does not appear to be the average online hacking group. In the report, the FBI points to similar attacks on South Korean and Middle Eastern businesses, including oil company Saudi Aramco, who lost 30,000 computers to the attack.

It is overwhelmingly likely to be a state-funded attack, which would be a first against the U.S. Various reports have said China and the U.S. are involved in a cyber warfare battle, but in the FBI report the countries North Korea and Iran pop up as possible countries sponsoring these attacks.

In another report earlier, a Sony executive claimed North Korea may have been behind the attack. The new film, The Interview, features Kim Jong-Un being assassinated - something the government in Pyongyang took exception over.

The malware attack was encoded in Korean, adding to the idea North Korea is behind the attack. This would put a lot of pressure on the U.S., to defend its companies against government attacks online.

The hackers responsible have already releases a lot of the data, including visa, passwords and business transactions/budgets for movies. One new movie coming from Sony Pictures has been leaked onto the web - and torrented thousands of times already.

Sony claims they have "restored a number of key services" with the help of FireEye's Mandiant service.

TagsFBI, sony, U.S. companies, North Korea, Malware, cyber espionage, Cyber Security