Unknown hackers stole $6 million from a Russian bank last year in an attack using the SWIFT international payments messaging system, the Russian central bank said.

The disclosure, buried at the bottom of a central bank report on digital thefts in the Russian banking sector, is the latest in a string of attempted and successful cyber heists using fraudulent wire-transfer requests.

The central bank said it had been sent information about “one successful attack on the workplace of a SWIFT system operator”.

A central bank spokesman said hackers had taken control of a computer at a Russian bank and used the SWIFT system to transfer the money to their accounts.

The spokesman declined to name the bank or provide further details. He quoted Artem Sychev, deputy head of the central bank’s security department, as saying this was “a common scheme”.

A spokeswoman for SWIFT, whose messaging system is used to transfer trillions of dollars each day, said the company does not comment on specific entities.

SWIFT claims hackers have never compromised its systems.

Brussels-based SWIFT said late last year digital heists were becoming increasingly prominent as hackers use more sophisticated tools and techniques to launch new attacks.

In December, hackers tried to steal 55 million roubles from Russian state bank Globex using the SWIFT system, and digital thieves made off with $81 million from Bangladesh Bank in February 2016.