"Cleanup" Apps: Playing Dirty
All too often when I'm analyzing a client computer, I find that the owner has installed one of the many unnecessary "cleanup" programs that purport to keep Macs healthy. (These include apps like MacKeeper, CleanMyMac, and others of that ilk.) You actually don't need anything like that on your system, and in fact, those types of applications can cause all sorts of trouble on their own.
For starters, how would something like that get on your system? Well, a lot of those programs use unethical methods (like pop-up ads or fake warnings) to scare you into installing them. If you've ever seen a huge "YOUR MAC IS INFECTED" banner in Safari, you know what I mean. (Those are always lies, just so you know.)
Another way this could happen is that you've gone looking for a legitimate app but downloaded it unknowingly from the wrong site. On sites that aggregate software from a bunch of different developers, the apps you do want are often bundled with stuff you definitely don't. When you install one of those malicious bundles, you may start seeing extra warnings, pop-ups, dialog boxes demanding you scan your computer for viruses, and so on. Sites to avoid because of this include Softonic, CNET, and MacUpdate. If you need a specific piece of software, make sure you're actually getting it from either the developer's site or from the Mac App Store just to be safe.
So let's say that you've gotten something unwanted on your computer and need to remove it. If that's the case, the first step would be to run screaming…no. Not that. You'll download and install Malwarebytes, which is an excellent (and legitimate!) program that'll let you run free scans to clean out anything nefarious. If it finds something bad, it'll give you instructions on how to remove it, which usually just involves a reboot.
After that, if you're still having trouble, you can check Safari for malicious extensions. You could also go through your Applications folder and move any of those questionable apps to the trash, although because many of them store files all around your system, this won't get rid of all of the pieces. If you'd like to make sure an app is well and truly gone, you may have to do a web search for "[name of bad program] uninstall Mac" or something of that nature. If you do that, just be sure the site you're clicking on for instructions isn't in and of itself questionable! Stick with the well-known Mac journalism sites, like Macworld.com and Macrumors.com (or of course anything on Apple's support pages).
Stay safe, folks. The Internet is no longer new, but it is certainly still a jungle out there, and it's super-easy to install something you don't want on your Mac. Give us a buzz if you need help with cleaning up the cleaner-uppers!