"This was an unprecedented attack," Sony chief executive Howard Stringer told reporters on Tuesday.

"A lot of these breaches are never reported by companies or it takes companies a month. You're telling me my week wasn't fast enough?"

The global Japanese electronics conglomerate said it expected to take monetary charges from the break-in.

"There's a charge for the system being down, a charge for identity theft protection," Stringer said. "The charges mount up but there are no numbers yet."