A joint advisory Thursday from the U.S. National Security Agency (NSA) and Britain's National Cyber Security Center said Russian military intelligence, the GRU, has been carrying out a "brute force" campaign since 2019 — getting hold of credentials, such as email logins, and then repeatedly guessing passwords until the hackers can gain entry. 

"After gaining remote access, many well-known tactics, techniques, and procedures (TTPs) are combined to move laterally, evade defenses, and collect additional information within target networks," the advisory said.   

The advisory noted that Russia's GRU has successfully targeted hundreds of U.S. and foreign organizations, as well as various U.S. government agencies, such as the Department of Defense. 

The Russians "directed a significant amount of this activity at organizations using Microsoft Office 365 cloud services; however, they also targeted other service providers & on-premises email servers," according to the advisory. "These efforts are almost certainly still ongoing." 

Elements of the campaign have previously been attributed to the Russian cyber actors known as Fancy Bear, APT28 or Strontium, but the NSA said Thursday that it felt compelled to share additional information on the attacks given the size of the ongoing operations.

"While the brute force techniques are not new, the distributed, highly scalable and anonymized nature of this brute forcing infrastructure highlights a persistent and increasing threat to the community," the agency told VOA in a statement.

U.S. officials urged agencies and organizations to take basic precautions as a first step in fighting back. 

"You can counter it by using strong authentication measures," NSA Cybersecurity Director Rob Joyce tweeted Thursday. "Adding multi-factor authentication will go a long way in remediating the threat." 

The NSA said other precautions, including time-out and lock-out features, could also help slow brute-force attacks and even "render them infeasible."

The brute-force attack advisory follows a string of high-profile hacks and ransomware attacks, including the December hack of SolarWinds, a U.S.-based software management company, which exposed as many as 18,000 customers to Russian hackers, and the May 7 ransomware attack against Colonial Pipeline, the largest fuel pipeline operator in the U.S. 

U.S. intelligence agencies have said the SolarWinds hack was part of a Russian operation, although cybersecurity experts say it was carried out by Russia's foreign intelligence service and not the GRU. 

U.S. officials have blamed the GRU for targeting the Democratic National Committee during the 2016 elections and the pharmaceutical companies developing vaccines against the coronavirus. 

"This is a good reminder that the GRU remains a looming threat," John Hultquist, vice president of analysis at the cybersecurity firm Mandiant Threat Intelligence, said in a statement Thursday. 

Hultquist added that the advisory was "especially important given the coming Olympics, an event they may well attempt to disrupt." But he also warned that "despite our best efforts, we are very unlikely to ever stop Moscow from spying."    

Some U.S. lawmakers have called for mandatory reporting requirements for companies hit by major hacks, ransomware attacks and other types of breaches, saying it will help the government respond more effectively to cyber intrusions. 

The nation's new cyber director, Chris Inglis, has also warned that although too many malign actors are operating with impunity in cyberspace, many private sector companies have likewise failed to take the necessary precautions. 

"It may well be we need to step in and we need to regulate or mandate in the same way we've done that for the aviation industry or the automobile industry," Inglis told lawmakers during his confirmation hearing last month.