An October cyber attack on a service run by Nasdaq OMX Group (NDAQ) is now being investigated by the National Security Agency amid signs the breach may have been more severe than previously disclosed, according to a new published report.

The inclusion of the NSA, the top U.S. electronics intelligence agency, may help investigators determine what was taken and who committed the crime, Bloomberg’s BusinessWeek reported. 

The cyber attack in question occurred in October and was first revealed by Nasdaq OMX Group, the parent of the Nasdaq Stock Market, in February.

Nasdaq said at the time that only a confidential document-sharing service it runs, called Directors Desk, had been hacked into and no data or documents appeared to have been taken. However, a source told BusinessWeek the attack was more extensive than Nasdaq previously disclosed.

Bringing in the NSA may show the Nasdaq attack endangered the security of the U.S.’s financial infrastructure, BusinessWeek reported.

“By bringing in the NSA, that means they think they’re either dealing with a state-sponsored attack or it’s an extraordinarily capable criminal organization,” Joel Brenner, former head of U.S. counterintelligence in the Bush and Obama administrations told the magazine. He also said the NSA rarely gets involved in probing cyber attacks against companies.

Foreign intelligence agencies are also said to be involved in the investigation, which may take months to complete.

The Nasdaq hack alarmed the security community because it was apparently aimed at an online portal run by a major stock market operator and used by boards of directors to remotely access documents, calendars and secure email.

When the breach was first disclosed, security experts were focused on at least three possible malicious intents behind the attack: a criminal gang searching for data to be used for insider trading, a state actor like China looking for economic intelligence or a group testing the waters before a larger-scale attack intended to disrupt the financial markets.

“While economics and leverage in insider trading was probably the goal here, an attack against the exchange systems themselves that brought them down, or worse -- corrupted recorded trades -- is all within the realm of feasible, if not likely,” Anup Ghosh, founder of security firm Invincea told FOX Business last month.

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