The internet attack is believed to have been connected with a âRussian cyber gangâ and aimed at Citigroup's Citibank subsidiary, the Wall Street Journal claimed.
Hackers were found to have targeted the bankâs computer system during the summer although the attack could have originally taken place the previous year.
Two other IT systems, one of which belonged to a federal agency, are reported to have been victims of the hack.
However, Joe Petro, managing director of Citigroup's Security and Investigative services, told the news provider that the hack never took place.
"We had no breach of the system and there were no losses, no customer losses, no bank losses. Any allegation that the FBI is working a case at Citigroup involving tens of millions of losses is just not true," he explained.
The news providerâs source claimed that an investigation into the alleged incident is being undertaken by the FBI and the National Security Agency, as well as Citigroup itself.
By Jim Ottewill