Do not install MacKeeper
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 has been described by various sources as highly invasive malware* that can de-stablize your operating system, adding that it is unethically marketed, with a history of making false advertising claims, by a company called Zeobit, and a rip-off.
(Please note that references to the original developers, Zeobit, also now refer to Kromtech Alliance Corp, who acquired MacKeeper and PCKeeper from ZeoBit LLC in early 2013.)
Most positive reviews of it have been found to have been paid for by Zeobit (developers of MacKeeper) in the form of ‘free upgrades’ etc. One such opinion is:
http://themacschool.blogspot.co.uk/2012/09/mackeeper-is-scam.html
For more about ‘astruturfing’ (writing phoney product reviews for money) see here:
http://en.wikipedia.org/wiki/Astroturfing
and http://www.bbc.co.uk/news/technology-24299742
Further opinion on it and how to uninstall MacKeeper malware can be read here:
http://applehelpwriter.com/2011/09/21/how-to-uninstall-mackeeper-malware/
MacKeeper have recently said that the uninstaller from here:
http://applehelpwriter.wordpress.com/2011/09/21/how-to-uninstall-mackeeper-malwa re/
now works.
There are many forms of ‘Malware’ that can affect a computer system, of which ‘a virus’ is but one type, ‘trojans’ another. Using the strict definition of a computer virus, no viruses that can attack OS X have so far been detected 'in the wild', i.e. in anything other than laboratory conditions. The same is not true of other forms of malware, such as Trojans. Whilst it is a fairly safe bet that your Mac will NOT be infected by a virus, it may have other security-related problem, but more likely a technical problem unrelated to any malware threat.
You may find this User Tip on Viruses, Trojan Detection and Removal, as well as general Internet Security and Privacy, useful: The User Tip seeks to offer guidance on the main security threats and how to avoid them.
https://discussions.apple.com/docs/DOC-2435
More useful information can also be found here:
www.thesafemac.com/mmg
* The expression ‘malware’ is a general term used by computer professionals to mean a variety of forms of hostile, intrusive, or annoying software.