As many others have said on this question, MacKeeper is not malware, but it could be called NAGWARE. I got sucked into buying a "Lifetime License" some time back. It appeared to be a nice utility and it was offered at an attractive discount through a what I thought was a reputable company, Smith Micro, the providers of the well known StuffIt compression software.
A few months back I found that after an update I started to receive notices advising me that the MacKeeper required a license as it was in demo mode. I wrote to them, only to be advised as follows:
"Please be informed that we have released new application MacKeeper 2012. You can upgrade your 2011 version here #### (I have blanked out the URL as I have no wish to promote their product) for additional $19.95, note that it has much more advanced Antivirus engine, a more sophisticated Files recovery feature and lots of more improvements.
Kindly be informed that MacKeeper 2012 is another application similar with MacKeeper 2011.
Althought you have purchased MacKeeper 2011 for a life time and you will be receiving all the updates for Mackeeper 2011 free of charge."
Of course they have stopped maintaining the 2011 version, so the last statement is pointless.
I chose not to upgrade but did not uninstall the app immediately. What has followed is a persistent notification that pops up in such a way that it looks like a Growl notification, the solution to which was to remove the software for which I had paid a license fee - it is almost impossible to continue to use it with the nag screen that could only be removed by uninstalling the software. Not unusual for these guys to copy the Growl notification style, if you read other messages in this list, you will find examples of them attempting, often successfully to immitate others to achieve their own financial success.
I have sent an email to Smith Micro advising them of what I think of MacKeeper. I have received no response and they continue to promote MacKeeper. I am not sure if there is a link or they just enjoy getting the revenue from the MacKeeper advertising. Either way, they have gone way down in my estimation.
This, together with other practices that you will find in the messages here, just indicate that these guys have ethics that are lower to the ground than a worms backside.
My advice.....avoid them like the plague.