Sentinel One says that since November of last year, it's seen more than 150 new strains of AdLoad, with "a sharp uptick throughout July and in particular the early weeks of August 2021."
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Many of the new strains evade the protections provided by Apple's Gatekeeper verification screener because the malware is "signed" with an Apple developer certificate.
They also dodge Apple's XProtect malware scanner, because many of the AdLoad strains don't match the malware profiles in XProtect's database. Some are also "notarized" to get past Apple's newest layer of defenses.
"The fact that hundreds of unique samples of a well-known adware variant have been circulating for at least 10 months and yet still remain undetected by Apple's built-in malware scanner demonstrates the necessity of adding further endpoint security controls to Mac devices," says Sentinel One.
What you can do to protect yourself
You're going to need one of the best Mac antivirus programs to stop this one, as Apple's own protections often won't be enough.
You could, in theory, prevent an AdLoad infection by refusing to provide your admin password when the malware begins the installation process.
But like most Mac malware, it will try to fool you into authorizing its installation by pretending your password is needed for some other reason. For example, an earlier Sentinel One report notes that AdLoad installers often masquerade as Adobe Flash Player installers.
How AdLoad works
AdLoad makes money by redirecting your web traffic. It takes over your browser's search-engine results and points them to sites that may pay AdLoad's creators a fee, and also injects its own set of ads on top of legitimate web ads.
That's not the worst kind of malware infection to have, but AdLoad also burrows into the operating system to make sure it's difficult to remove. And if this kind of middleweight Mac malware makes it on to your machine, who knows what kind of more serious infections you could also have?
"The good news for those without additional security protection is that the previous variant we reported in 2019 is now detected by XProtect," says Sentinel One's newer report. "The bad news is the variant used in this new campaign is undetected by any of those rules."
Apple has been revoking the developer certificates as soon as it spots an AdLoad strain, but "we see new samples signed with fresh certificates appearing within a matter of hours and days," says the report.
"Truly, it is a game of whack-a-mole."
This story was earlier reported by Bleeping Computer.