Hackers released documents and files on Friday that cybersecurity experts said indicated the U.S. National Security Agency had accessed the SWIFT interbank messaging system, allowing it to monitor money flows among some Middle Eastern and Latin American banks.

The release included computer code that could be adapted by criminals to break into SWIFT servers and monitor messaging activity, said Shane Shook, a cyber security consultant who has helped banks investigate breaches of their SWIFT systems. The documents and files were released by a group calling themselves The Shadow Brokers.

Cyber attacks targeting the global bank transfer system have succeeded in stealing funds since February’s heist of $81 million from the Bangladesh central bank as hackers have become more sophisticated in their tactics, according to a SWIFT official and a previously undisclosed letter the organization sent to banks worldwide.

The messaging network in a Nov. 2 letter warned banks of the escalating threat to their systems, according to the SWIFT letter. The attacks and new hacking tactics underscore the continuing vulnerability of the SWIFT messaging network, which handles trillions of dollars in fund transfers daily.

A Ukrainian bank has become the latest victim of the widespread cyber attack on global banking and financial sector by hackers who target the backbone of the world financial system, SWIFT. Hackers have reportedly stolen $10 Million from an unnamed bank in Ukraine.

Swift or the Society for Worldwide Interbank Financial Telecommunication is the global banking messaging system responsible for managing Billions of dollars in money transfers each day between financial institutions worldwide. The ISACA branch in Ukraine disclosed that some unknown hackers were able to compromise the bank's security in similar way they hacked Bangladesh central bank.

Bangladesh's central bank was vulnerable to hackers because it did not have a firewall and used second-hand, $10 switches to network computers connected to the SWIFT global payment network, an investigator into one of the world's biggest cyber heists said.

The shortcomings made it easier for hackers to break into the Bangladesh Bank system earlier this year and attempt to siphon off nearly $1 billion using the bank's SWIFT credentials, said Mohammad Shah Alam, head of the Forensic Training Institute of the Bangladesh police's criminal investigation department. "It could be difficult to hack if there was a firewall," Alam said in an interview.