Browser Hijacking: the WeKnow.ac Malware

I was helping a client with a few issues on her Mac, when I noticed odd behavior in the web browser on her machine. In the space of a few moments, I saw:

• An “update your Adobe Flash” install popup window (NEVER do this!!!!)
• Another popup window trying to sell software by scumbags (MacKeeper semi-malware).
• Two folders containing shell scripts that wrote to /tmp, enable execute permissions and executed some script.
• Safari was hijacked in a way that prevented setting any home page, and the default page was set to the web site "weknow.ac" (don’t visit it!).

From what I could tell, the problem started from her having clicked on an “Update Flash” prompt that came from an infected website.

Her machine was infected with the WeKnow.ac malware. It does all sort of annoying things but the main thing is that much worse things are likely to result from it via information stealing, redirection to dangerous web sites, etc. This page at macpaw.com has a good how-to remove WeKnow.ac without frequently trying to sell you new software to fix it.

I was able to clean up the mess, but most people will have trouble doing so. There are lots of "how to" cleanup pages, most of which push anti-virus software (which MPG is at best ambivalent on and does not recommend). Don’t panic and find an expert to help you (does Apple help with such stuff?) or research fixit software and the company selling it before buying anything.

Downloading software that purports to remove WeKnow.ac is itself a risk—how would you know that it itself is not malware?! Certainly do not click through any link on a fixit page. Research it separately if you want to use other software to fix it.

Question for Apple: what is wrong with macOS that it allows this kind of well-known longstanding malware to infect a computer?