A second hacking group is also trying to rob banks by exploiting the SWIFT money transfer system, following a US$81 million heist in February that used a similar approach.
The cyberattacks have been going on since January and have been targeting companies in the U.S., Hong Kong, Australia, and other countries, according to a Tuesday report from security firm Symantec.
A "rough guess" is that about 100 organizations have been hit so far, based on the 74 individual computer infections detected, the security firm added.
As part of their attacks, the hackers used malware to cover up records of fraudulent transactions made over SWIFT, preventing their victims from learning about the money theft.
Symantec said this approach bears a resemblance to the February heist at a Bangladesh bank that also involved hackers hiding evidence of their attack by tampering with the SWIFT system.
Some security experts have blamed the Bangladesh heist on the Lazarus Group, which has been linked to the North Korean government and the infamous 2014 hack of Sony pictures. However, Symantec said the malware used in these newly uncovered attacks probably belong to a separate cybercriminal gang known as Carbanak, which is believed to have stolen over $1 billion from dozens of countries by facilitating large wire transfers.
"This new wave of attacks has also used some infrastructure that has previously been used in Carbanak campaigns," Symantec said. This includes the use of IP addresses found in previous Carbanak-related attacks.
To target their victims, the hackers distributed Microsoft Word documents and RAR archives -- likely through email phishing -- that can secretly install a Trojan onto a target computer. That Trojan can then load other hacking tools built to recover passwords and execute programs.
The hackers were targeting financial organizations in the banking, securities, trading, and payroll sectors, but they also attacked a small number groups related to the government, healthcare, and legal industries.
"Although difficult to perform, these kinds of attacks on banks can be highly lucrative," Symantec said. "Estimates of total losses to Carbanak-linked attacks range from tens of millions to hundreds of millions of dollars."
On Tuesday, SWIFT, or the Society for Worldwide Interbank Financial Telecommunication, said it's aware of the details in Symantec's report. In August, it warned customers about ongoing attacks and has been publishing details on how to prevent them.