Sony may not have thought the PSN was a target for hackers due to its nature as a free service.
Sony did its users a solid in this console generation by making its online service, the PlayStation Network, completely free. In light of the recent PSN hack attack that took Sony's servers down for more than three weeks, CEO Howard Stringer seems a little caught off-guard that his company was helping gamers out with a free service which then got hacked.
"We have a network that gave people services free," Stringer told Bloomberg. "It didn't seem like the likeliest place for an attack."
He added that Sony believed it had "good, robust security." Even if true, Stringer's comment seems to hint that Sony may have had a mindset of "we scratch your backs, you scratch ours" when it came to PSN security because the service was free.
However, at the same time Sony was removing features like Other OS, and suing George "GeoHot" Hotz, known for cracking the PlayStation 3's rootkey. This set off a flame of criticism, notably from Anonymous, which launched an operation against Sony but claimed it had nothing to do with the server intrusion that brought down the PSN.
It was definitely a jerk move to hack into the PSN and possibly remove personal information (which hasn't been confirmed yet), but that's the way of the internet even without Sony inflaming people's opinions against it in these various ways. People will hack into anything nowadays, so if you taunt them it's all but assured. All we can do is hope that Sony learned its lesson and will do everything it can to prevent future attacks.