(Reuters) - Russian hackers had infiltrated Dow Jones & Co to steal information to trade on before it was made public, and the breach was "far more serious than a lower-grade intrusion" disclosed by the company last week, Bloomberg reported, citing sources.
The Federal Bureau of Investigation, Secret Service and the Securities and Exchange Commission are leading an investigation, which began at least a year ago, Bloomberg reported.
Dow Jones, the publisher of the Wall Street Journal, said last week a breach of its systems that put payment card and contact information of about 3,500 individuals at risk.
"We are aware of the Dow Jones intrusion and looking into it," FBI spokeswoman Kelly Langmesser said via email.
Dow Jones and the Secret Service could not be immediately reached for comment. The SEC declined to comment.
(Reporting by Supantha Mukherjee and Joseph Menn; Editing by Savio D'Souza)