According to The Wall Street Journal, U.S. authorities are investigating a computer-security breach targeting Citigroup.Inc. The hackers, who appear to be linked to a Russian cyber gang, made away with tens of millions of dollars.

It's unknown whether the hackers gained direct access to Citibank's systems or if they went through a third party, or if it even happened at all. Despite reports to the contrary, Citibank officals contend that no such breach occurred.

"We had no breach of the system and there were no losses, no customer losses, no bank losses," said Joe Petro, managing director of Citigroup's Security and Investigative services. "Any allegation that the FBI is working a case at Citigroup involving tens of millions of losses is just not true."

The Wall Street Journal claims the threat was initially detected by U.S. investigators who noted suspicious traffic from IPs that had been used by the Russian Business Network, which is a Russian gang that has a history of selling hacking tools and software for accessing U.S. government systems.