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 was iAntivirus:
until it was purchased recently (May 2012) by Symantic (makers of Norton anti-virus which does not work well with Apple OS X). Even after having tinkered with it, iAntivirus still fails to do the job properly and cannot be recommended.
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. Note, however, that Trojans are another matter and can represent a genuine threat, an example of which was the recent 'Flashback Trojan' which you can read more about here:
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.
* The expression ‘malware’ is a general term used by computer professionals to mean a variety of forms of hostile, intrusive, or annoying software.