Just cleaned out a system that had malicious profiles installed the other day. There is a pane in System Preferences called “Profiles” that contains a bunch of, well, profiles. It's normally not visible, and I'm honestly not sure whether it's a legitimate pane or something installed by malware. In any case, it somehow allows the OS to control certain aspects of various applications; in this case, it set the default search engine for Google Chrome to some adware site. Attempts to change that setting in Chrome failed, with Chrome stating that the search engine setting was enforced by the network administrator. Anyway, after deleting all of the “profiles” in the Profiles pane, the search engine enforced setting was released, and I was able to reset it to the default of Google (so much for eliminating adware…). Interestingly, once the profiles were all removed, the Profiles pane disappeared from System Preferences.
The insidious part is that there was also apparently a startup .plist that installed a new copy of the profile; I'm guessing that is the reason why I saw the same profile installed 8 or 9 times (once for every reboot since the malware had been activated). I only discovered that because I decided to install and run Malwarebytes, which I have to say did its job in this case, and for free at that (they charge for continuous monitoring or something, but the free version is perfectly adequate for detecting and removing malware). Malwarebytes was able to detect and remove the malicious .plist, and I'm reasonably confident that it was purged from the system entirely.
Not trying to sound like a shill for Malwarebytes here, but I was actually pretty impressed. I wouldn't pay for it myself, but I can see paying for a subscription for someone who is less computer-savvy, if only so you don't have to spend time cleaning crap like that out on the regular.