A group of Russian hackers were reported to have hacked Dow Jones & Co. servers in pursuit of embargoed market-moving information more than a year ago.

Bloomberg said that the attack was “far more serious” than the data breach disclosed by Dow Jones last week, quoting sources familiar with the situation.

The sources told Bloomberg the FBI, Secret Service and the Securities and Exchange Commission (SEC) are investigating the hack.

In August, five traders in Georgia and Pennsylvania were arrested as part of a scheme of up to 32 stock traders and hackers who breached the computer servers of PRNewswire Association LLC, Marketwired and Business Wire.

Dow Jones chief communications officer Ashley Huston told SCMagazine.com via email, “Since Bloomberg published its article, we have worked hard to establish whether the allegations it contains are correct. To date, we have been unable to find evidence of any such investigation.”