(Bloomberg) — A previously unknown ring of Russian-language hackers has stolen as much as $10 million from U.S. and Russian banks in the last 18 months, according to a Moscow-based cyber-security firm that runs the largest computer forensics laboratory in eastern Europe.

The MoneyTaker group broke into 20 systems, which includes 15 U.S. lenders, targeting ATMs with “mules” and Russia’s interbank money-transfer system, Group-IB said in a report provided to Bloomberg.

The hackers, who also breached a U.K. software and service provider, are now probing institutions in Latin America and may be trying to compromise the Swift international bank messaging service, according to the security firm, whose clients range from Russia’s biggest lender Sberbank PJSC to Raiffeisen Bank International AG.

“Criminals have changed tactics and are now focusing on banks rather than their clients, as was the standard operating procedure in the past,” Dmitry Volkov, the head of Group-IB’s cyber intelligence department, said by phone.

Russia, considered a hotbed of government-backed information attacks, increasingly finds itself a victim of cybercrime. It took the initial blame for the Badrabbit ransomware virus that spread to more than 200 targets globally, even though some of the biggest disruptions affected Russian businesses.

‘Limited Resources’

Since its first successful breach in May 2016, MoneyTaker has stolen from banks in New York, California, Utah and Moscow, primarily targeting smaller institutions with limited cyber defenses, Group-IB found. The average haul from U.S. banks was about $500,000, and it stole over $3 million from three Russian lenders.

“They understand that banks — especially community banks with limited resources — are the easiest marks,” Volkov said.

The cell remained undetected by using so-called fileless malware that only exists on a computer’s temporary memory and destroys itself when the system reboots, meaning it’s not permanently stored and therefore can more easily evade anti-virus programs, according to Group-IB.