I wish I could remember the HN thread, but another HNer who claimed to have worked for Sony Picture's security described the security system as non-existent and was surprised that it hadn't happened sooner... Now to go looking for that.
And any of us who've worked in a corporate environment know that Sony is by no means exceptional in that respect. There are security vulnerabilities all over cyberspace just waiting for someone to exploit them (just as in real life). We're protected mainly by some combination of good will, disinterest, and fear of punishment (also as in real life).
Even if their security system was poorly constructed, they're still victims of cyber terrorism.
I have to take exception with the term terrorism here. They were victims of cyber crime, sure.
Not necessarily Sony, but the last missives threatening 9/11-style attacks on movie theaters would count as terrorism. Up until that point it was a hacking scandal against Sony. Once you start threatening the movie-going public, then you move into terrorism.