How did CleanMyMac get on my iMac and how do I get rid of it?

Question

Recently this app showed up. I didn't download it intentionally. Is it part of the OS or just adware / malware? How do I get it off the Mac?

Answer 1

Unless you download it there is no way for it to get on your computer.
If you find an uninstaller for it in your Applications folder or in the original media then use it. Otherwise, I recommend:
Uninstalling Software: The Basics
Most OS X applications are completely self-contained "packages" that can be uninstalled by simply dragging the application to the Trash.  Applications may create preference files that are stored in the /Home/Library/Preferences/ folder.  Although they do nothing once you delete the associated application, they do take up some disk space.  If you want you can look for them in the above location and delete them, too.
Some applications may install an uninstaller program that can be used to remove the application.  In some cases the uninstaller may be part of the application's installer, and is invoked by clicking on a Customize button that will appear during the install process.
Some applications may install components in the /Home/Library/Applications Support/ folder.  You can also check there to see if the application has created a folder.  You can also delete the folder that's in the Applications Support folder.  Again, they don't do anything but take up disk space once the application is trashed.
Some applications may install a startupitem or a Log In item.  Startupitems are usually installed in the /Library/StartupItems/ folder and less often in the /Home/Library/StartupItems/ folder.  Log In Items are set in the Accounts preferences.  Open System Preferences, click on the Accounts icon, then click on the LogIn Items tab.  Locate the item in the list for the application you want to remove and click on the "-" button to delete it from the list.
Some software use startup daemons or agents that are a new feature of the OS.  Look for them in /Library/LaunchAgents/ and /Library/LaunchDaemons/ or in /Home/Library/LaunchAgents/.
If an application installs any other files the best way to track them down is to do a Finder search using the application name or the developer name as the search term.  Unfortunately Spotlight will not look in certain folders by default.  You can modify Spotlight's behavior or use a third-party search utility, EasyFind, instead.
Some applications install a receipt in the /Library/Receipts/ folder.  Usually with the same name as the program or the developer.  The item generally has a ".pkg" extension.  Be sure you also delete this item as some programs use it to determine if it's already installed.
There are many utilities that can uninstall applications.  Here is a selection:
    1. AppZapper
    2. AppDelete
    3. Automaton
    4. Hazel
    5. AppCleaner
    6. CleanApp
    7. iTrash
    8. Amnesia
    9. Uninstaller
  10. Spring Cleaning
For more information visit The XLab FAQs and read the FAQ on removing software.