A PlayStation Blog post summarizes the content of the letter. According to Hirai, Sony has worked under the following four principles in dealing with the issue: "Act with care and caution, " "Provide relevant information to the public when it has been verified," "Take responsibility for our obligations to our customers," and "Work with law enforcement authorities."
In addition, the letter and post provide a timeline of the attack, including this early clue: "We discovered that the intruders had planted a file on one of our Sony Online Entertainment servers named 'Anonymous' with the words 'We are Legion.'" Despite that evidence, Sony still says it has yet to identify the "individual(s) responsible for the breach." It's unclear if that means Sony does not think the hacking organization known as Anonymous was responsible or, rather, if it hasn't managed to uncover the actual identities of Anonymous' ... err, anonymous contributors.
The "Welcome Back" program was also detailed, through which Sony is offering free downloads, and free PlayStation Plus memberships (and Qriocity access for those subscribers) lasting 30 days plus the length of the PSN outage.