But the White House was not ready to put the blame on North Korea, despite a U.S. official's indication on Wednesday that Washington may soon formally announce the involvement of the Pyongyang government.
               
President Barack Obama was monitoring the cyberattack very closely, White House spokesman Josh Earnest said. But even as the White House studied a "proportional response," experts warned that the effect of strategies like cyber retaliation or financial sanctions could be limited.
               
The attack more than three weeks ago by hackers identifying themselves as "Guardians of Peace" is the biggest hacking of a company on U.S. soil and might be repeated with other companies.
               
It brought down the computer network at Sony Pictures Entertainment, prompted the leak of embarrassing emails, and led to a film cancellation that many in Hollywood and Washington said was tantamount to caving in to the hackers.
               
Sony decided on Wednesday to scrap its big Christmas Day release of "The Interview," a comic film that culminates in the assassination of North Korean leader Kim Jong Un, a scene that was leaked on the Internet on Thursday.
               
Sony pulled the film after movie theater chains said they would not show the film citing security concerns after hackers made threats against cinemas and audiences.
               
A senior North Korean U.N. diplomat declined to comment on accusations that Pyongyang was responsible for the hacking attack on Sony Pictures.
               
NBC News reported on Thursday night that U.S. Officials believe the attack was launched in North Korea and then routed through servers in Taiwan to take advantage of faster computer circuits.