The Federal Bureau of Investigation has confirmed it is investigating a hack into Sony Pictures Entertainment's network last week.

The hack took down the firm's email systems and paralysed its network.

A group called Guardians of Peace took credit for the attack, flashing the message "hacked by #GOP" on screens.

The FBI said that "the targeting of public and private sector computer networks remains a significant threat.''

Previously, Sony has said the firm was investigating the "IT matter".