Two years since the WannaCry attacks wreaked havoc on computer systems around the world, researchers say hundreds of thousands of people are being targeted with the EternalBlue exploit on which it was based.

Though patches have long been available to deal with the flaw in Microsoft’s Server Message Block (SMB) implementation on Port 445, cybercriminals continue to make use of EternalBlue, which was first developed by the U.S. National Security Agency before it was leaked and stolen.

A recent blog post from ESET showed that attempts to block attacks based on the exploit have skyrocketed this year, according to ESET telemetry data. While WannaCry represents one of the more successful attempts to take advantage of EternalBlue, cybercriminals are clearly hoping history will repeat itself.

The Potential Return of WannaCry

ESET researchers said that China has recently been targeted by EternalBlue-based attacks that use malware to mine cryptocurrency by stealing a computer’s resources. This is somewhat different from how the flaw was exploited by WannaCry, as well as NotPetya and BadRabbit, which followed not long after in 2017.

Despite the worldwide attention the WannaCry attacks brought to the importance of following IT security best practices, researchers suggested that there are still many firms that have not deployed the patches available to them.

There are also fresh instances of EternalBlue in the wild exploiting other vulnerabilities, including a remote desktop protocol (RDP) issue in certain versions of Windows, according to a post from researchers at Malwarebytes Labs. While the attack on this vulnerability is not officially named, it performs in a familiar way — threat actors don’t need to infect a particular system; they can execute code remotely and hold it for ransom. Microsoft has since issued a patch to deal with the exploit.

Researchers added that some of the uptick in EternalBlue activity may not be malicious, but instead the result of attempts by corporate security teams to experiment with the exploit and perform penetration testing so they can fend off WannaCry-style attacks better in the future.

Stop the Next WannaCry With a Least Privilege Approach

Fortunately, there are plenty of existing ways for organizations to protect themselves from EternalBlue-based cyberattacks. IBM experts suggest starting by adopting a least privilege approach to network access, reviewing network isolation policies and deactivating any outdated SMB protocols.