"fairly large amount of data" had been made vulnerable on April 25th (US time).
However they didn't announce until the next day and downplayed the severity, stating they couldn't "rule out the possibility" personal data was breached.
PlayStation head Kaz Hirai gave out 'false information' claims the report in a statement on May 1st, in which Sony said they didn't know how far reaching the hack was on PlayStation Network until April 26th, the day after Sony knew internally what happened.
"We hadn't figured out (at that time) what kind of data had been leaked. If only passwords and IDs (were breached), they cannot be considered personal information, and so we didn't want to bewilder our customers," said a Sony spokesperson, revealed the documents.
Kyodo News claims that Sony "deliberately attempted to downplay the seriousness of the situation by not fully disclosing information", and that's why the Japanese government has been harsh in dealing with the breach and demanding additional assurances.
As they say 'it's the cover up, not the crime'. Since the now almost 'historic' hack of PSN a wave of cyber attacks have plagued the videogames industry with Sony in particular being targeted through their various corporate divisions.