Here's an important notice from John Carter: "It was just brought to my attention by Betsy Barnes that MacKeeper is one of the apps that you do not want to install on your Mac.
"The reasons are various. It has been described as highly invasive malware, but this is probably because it pops up in your face every time you drag an application to the trash (the preferred method is to use AppCleaner to delete an application), and then often after dragging anything to the trash.
"Malware is anything that is hostile, intrusive, or annoying. So if being reminded that MacKeeper can clean up your computer is annoying, then MacKeeper is malware. By this logic, Apple's Notification Center can be annoying and therefor it is malware.
"MacKeeper does this as a way of 'helping' you keep your computer running lean and fast. Does it really?
"A simple query in Safari returns dozens of complaints about MacKeeper. For one user who bought a MacBook Pro and then installed MacKeeper, he started having freezes and crashes. A scan of the logs clearly showed MacKeeper as involved in every crash and freeze (See the full report here.)
"Additionally, one user has attempted to get a refund and is still waiting for it after being told three times he will get it."
John concludes, "For what it's worth, I am no longer even suggesting that MacKeeper be used on a Mac. Use AppCleaner to remove apps and the rest can be trusted to just dumping it into the Trash.
For further reading, see this article on "Do not install MacKeeper."