Sony claims hackers targeted the firm because it tried to protect its intellectual property.

In April this year, the technology giant became the victim of an attack that saw the personal details of around 77 million gamers leaked to the web and resulted in Sony pulling the plug on the PlayStation Network and Qriocity music streaming service on 20 April. It took a month for the services to be restored.

"We believe that we first became the subject of attack because we tried to protect our IP (intellectual property), our content, in this case videogames," CEO Howard Stringer told shareholders this week.

"These are our corporate assets, and there are those that don't want us to protect them. They want everything to be free."

The hackers that launched the attack have yet to claim responsibility.