BOSTON — A global epidemic of digital extortion known as ransomware is crippling local governments, hospitals, school districts and businesses by scrambling their data files until they pay up. Law enforcement has been largely powerless to stop it.

One big reason: Ransomware rackets are dominated by Russian-speaking cybercriminals who are shielded — and sometimes employed — by Russian intelligence agencies, according to security researchers, U.S. law enforcement, and now the Biden administration.

On Thursday, as the U.S. slapped sanctions on Russia for malign activities including state-backed hacking, the Treasury Department said Russian intelligence has enabled ransomware attacks by cultivating and co-opting criminal hackers and giving them safe harbor. With ransomware damages now well into the tens of billions of dollars, former British intelligence cyber chief Marcus Willett recently deemed the scourge “arguably more strategically damaging than state cyber-spying.”

The value of Kremlin protection isn’t lost on the cybercriminals themselves. Earlier this year, a Russian-language dark-web forum lit up with criticism of a ransomware purveyor known only as “Bugatti,” whose gang had been caught in a rare U.S.-Europol sting. The assembled posters accused him of inviting the crackdown with technical sloppiness and by recruiting non-Russian affiliates who might be snitches or undercover cops.

Worst of all, in the view of one long-active forum member, Bugatti had allowed Western authorities to seize ransomware servers that could have been sheltered in Russia instead. “Mother Russia will help,” that individual wrote. “Love your country and nothing will happen to you.” The conversation was captured by the security firm Advanced Intelligence, which shared it with the Associated Press.

“Like almost any major industry in Russia, (cybercriminals) work kind of with the tacit consent and sometimes explicit consent of the security services,” said Michael van Landingham, a former CIA analyst who runs the consultancy Active Measures LLC.

Russian authorities have a simple rule, said Karen Kazaryan, CEO of the software industry-supported Internet…