US officials blame North Korea for the hacking, citing the tools used in the Sony attack and previous hacks linked to the North, and have vowed a response. The break-in resulted in the disclosure of tens of thousands of confidential Sony emails and business files, and escalated to terrorist threats that caused Sony to cancel the Christmas release of the movie "The Interview." The comedy is about a plot to assassinate North Korean leader Kim Jong Un.
    
On Saturday, an unidentified Foreign Ministry spokesman in Pyongyang said North Korea knows how to prove it's not responsible for the hacking, so the United States must accept its proposal for the joint investigation.
    
"The US should bear in mind that it will face serious consequences in case it rejects our proposal for joint investigation and presses for what it called countermeasures while finding fault with" North Korea, the spokesman said in a statement carried by Pyongyang's official Korean Central News Agency.
    
"We have a way to prove that we have nothing to do with the case without resorting to torture, as what the CIA does," he said.
    
On Friday, President Barack Obama declared that Sony "made a mistake" in shelving the satirical film about a plot to assassinate the North Korean leader, and pledged the US would respond "in a place and manner and time that we choose" to the hacking attack on Sony that led to the movie's withdrawal.
    
"I wish they had spoken to me first. ... We cannot have a society in which some dictator someplace can start imposing censorship," Obama said at a year-end news conference, speaking of executives at Sony Pictures Entertainment.
    
Sony said it had had no choice but to cancel distribution of the movie since theaters were refusing to show it.

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