Sony has been fined Ł250,000 - and the company's data protection policies criticised - by UK authorities investigating the infamous 2011 PlayStation hack.
The Information Commissioner's Office described the attack, which risked the personal information of 77 million customers, as a "serious breach of the Data Protection Act".
Hackers gained access to customer names, addresses, dates of birth and passwords. Payment card details were also left "at risk", the ICO described.
Sony has already said it "strongly disagreed" with the ICO's ruling and plans to appeal, BBC business editor Steph McGovern wrote.
The ICO's report concluded that the attack "could have been prevented" if Sony's security had been up-to-date.
"If you are responsible for so many payment card details and log-in details then keeping that personal data secure has to be your priority. In this case that just didn't happen," said David Smith, deputy commissioner and director of data protection. "When the database was targeted - albeit in a determined criminal attack - the security measures in place were simply not good enough.
"There's no disguising that this is a business that should have known better. It is a company that trades on its technical expertise, and there's no doubt in my mind that they had access to both the technical knowledge and the resources to keep this information safe.
"The penalty we've issued today is clearly substantial, but we make no apologies for that. The case is one of the most serious ever reported to us. It directly affected a huge number of consumers, and at the very least put them at risk of identity theft."
Sony boss Kaz Hirai was one of several high-ranking executives who personally apologised following the hack, which left all customers with a 24-day PlayStation Network outage while security was beefed up.