The FBI released a FLASH Alert about destructive malware on December 1st:
The destructive malware in question is a wiper similar to Shamoon. It uses the same benign driver for raw disk access.
On November 24th, this wallpaper was dropped on the computers of SPE employees:
Who is responsible for the attack?
North Korea has been suggested. That seems implausible to us.
The attackers apparently made demands:
• "We've already warned you, and this is just a beginning."
• "We continue till our request be met."
The demands have not yet been made public; when they were not met… the attackers dumped large amounts of SPE's data.
Theory: either the attackers are copyright reformist hackers targeting Hollywood — or — the attack was an attempted shakedown and extortion scheme. Hackers interested in copyright reform very often use better grammar than that found in the wallpaper above.
Which causes us to worry it's about extortion. And that's a big concern because it would mean the point of SPE's public "execution" was to warn to other companies that may already be hacked that the extortioners aren't bluffing.
Either way, Sony Pictures Entertainment may only be the first.
Edited: adjusted a sentence above to link to Shamoon.