Hackers shut down Sony's systems and then released an estimated 11 terabytes of data.

Stolen information was sent to reporters and is available to download online.

It's not clear who is responsible for the attack.

Here are some of the most eye-opening things we've learned so far:

• Sony thinks it was North Korea, Re/code reports. The new Seth Rogen and James Franco film "The Interview," a comedy about two men sent on a mission to assassinate North Korean dictator Kim Jong Un, is believed to be why the hack took place, since North Korea previously sought Sony to stop the release of that film. Rogen had no comment when asked about the incident by Business Insider.

Re/code reported last week that Sony is investigating whether hackers operating on behalf of North Korea were behind the attack. North Korean officials previously stated their opposition to the movie. 

• Experts say the hack is "the first major attack on a US company to use a highly destructive class of malicious software that is designed to make computer networks unable to operate," Reuters reports.