Researchers at Malwarebytes have found that a new variant to the SamSam ransomware has been hitting users wherein the attacker has to put in a password before the malware could be executed.

“In its time being active, SamSam has gone through a slight evolution, adding more features and alterations into the mix,” read the blog post by Malwarebytes Labs. “These changes do not necessarily make the ransomware more dangerous, but they are added to make it just a bit more tricky to detect or track as it is constantly changing.”

According to researchers, this variant does not go into effect without the password, even if the malware is already present in the system. This makes for a more “targeted” attack as the attackers can decide which computers to execute the ransomware on.

Aside from targeted attacks, it also means that only those who know the password can access the ransomware code or execute the attack, making it a tricky malware to understand.

“As analysts, without knowing the password, we cannot analyze the ransomware code. But what’s more important to note is that we can’t even execute the ransomware on a victim or test machine. This means that only the author (or someone who has intercepted the author’s password) can run this attack,” the blog post said on the issue.

“This is a major difference from the vast majority of ransomware, or even malware, out there,” the post went on to say. “SamSam is not the type of ransomware that spreads like wildfire. In fact, this ransomware quite literally cannot spread automatically and naturally.”

SamSam has been a part of several massive cyber attacks since early 2018 and has led to severe damages worldwide. This new variant has only made it more elusive, as the code is inaccessible even to security researchers, which might be another reason for the password requirement.

The ransomware has in the past targeted hospitals, state agencies, city councils, and other enterprises, and caused huge losses when it hit the IT network of Atlanta earlier this year.