Sony Said to Learn Last Year About Large Network-Security Breach

Sony Corp. was warned about a year ago that hackers had infiltrated its network and were stealing gigabytes of data several times a week, underscoring a pattern of lapses predating a recent attack that has spilled Sony Pictures’ secrets onto the Internet.

The hackers, who haven’t been identified, sifted in late 2013 through data from the company’s network, encrypted the information to cover their tracks and mined it on a regular schedule, said a person familiar with Sony’s investigation of the breach who asked not to be named because the findings are confidential.