“Sony declined to publicly disclose how the hacker gained access, saying the information might jeopardize an ongoing probe of the attacks and put other networks at risk, according to the May 26 letter to Representatives Mary Bono Mack, a California Republican, and G.K. Butterfield, a North Carolina Democrat.
Sony still doesn’t know who was responsible for the intrusion or precisely how much information was taken, the company said in the letter responding to questions from Bono Mack and Butterfield. The hacker took steps to cover tracks in and out of the company’s servers and conceal what data was taken, Sony said.
“
Source: Sony Says It May Know How Hacker Succeeded – Bloomberg