Washington - North Korea was responsible for a "destructive" cyber attack on Sony Pictures, the US Federal Bureau of Investigation said Friday, warning it would hunt down the perpetrators and make them pay."Such acts of intimidation fall outside the bounds of acceptable state behaviour," the FBI said in a statement, adding it would "identify, pursue, and impose costs and consequences on individuals, groups, or nation states who use cyber means to threaten the United States or US interests".The attack prompted the movie giant to cancel the Christmas Day release of The Interview, a madcap satire about a fictional CIA plot to kill North Korean leader Kim Jong-Un.Hackers had invoked 9/11 in threatening attacks on cinemas screening the film.In addition to the violent threats, Sony has seen the release of a trove of embarrassing emails, scripts and other internal communications, including information about salaries and employee health records."We are deeply concerned about the destructive nature of this attack on a private sector entity and the ordinary citizens who worked there," the FBI said.A Sony source had told AFP that the studio believed Pyongyang was behind it."We don't know, but it appears so," said the source.The FBI said the attack involves the use of malware and rendered thousands of Sony Pictures computers "inoperable", forcing the company to take its entire network offline."The FBI now has enough information to conclude that the North Korean government is responsible for these actions," it said.