FBI to Link North Korean Government to Sony Hack Attack

The FBI has officially accused North Korea of the Sony hack, with a statement expected later. The US government is considering its response options, which are limited due to the difficulty of targeting North Korea's cyber infrastructure. The US may focus on naming and shaming North Korea to draw international attention. President Obama is expected to address the issue in a news conference.

What is the significance of the FBI's statement expected later today?

What challenges does the U.S. face in targeting North Korean infrastructure?