Many users will see references to an application called MacKeeper on various web sites and via pop-ups on their browser. Not only is it expensive for what it purports to do (freeware applications that do the same or more are readily available), it can sometimes install itself without the user realising it, and it can be very tricky to get rid of.
MacKeeper can be regarded as highly invasive malware* that can de-stablize your operating system. It is unethically marketed by a company called Zeobit and a rip-off.
Further opinion on it and how to uninstall MacKeeper malware can be read here:
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:
There are no viruses that can affect Apple OS X and there is therefore no reason to run anti-virus software on a Mac, but a Mac, like all computers, can transmit viruses and malware to other users particularly those running Windows.
For further information you may find this User Tip on Viruses, Trojan Detection and Removal, as well as general Internet Security and Privacy, useful:
The User Tip (which you are welcome to print out and retain for future reference) seeks to offer some guidance on the main security threats and how to avoid them.
ds store addition:
Note: MacKeeper is also known as the "911 Bundle" on the MacAppStore
Manual uninstall instructions also here
* The expression ‘malware’ is a general term used by computer professionals to mean a variety of forms of hostile, intrusive, or annoying software.