MacKeeper, being poorly written, acts like highly invasive malware* that can de-stablize your operating system. It is also unethically marketed and a rip-off, offering nothing that is not available for free.. Positive reviews of it are known to have been paid for by the developers, Zeobit.
Further opinion on it and how to uninstall MacKeeper malware:
Do NOT download or use the ‘MacKeeper uninstaller’ from the Zeobit site, as this will cause even more damage to your operating system.
This is also worth reading:
Equally phoney is iAntivirus:
* The expression ‘malware’ is a general term used by computer professionals to mean a variety of forms of hostile, intrusive, or annoying software.