Ex-Windows expatriates are so used to having to use applications such as MacKeeper on their old Windows computers they were natural targets for such an application that offered anti-virus, anti-malware, housekeeping utilities to keep their new Mac clean and working up to speed they naturally thought they needed something just like it and bought it. . . unaware that Apple OS X on their Macs needed none of those things. In fact, MacKeeper TURNED OFF the built-in utilities that did all that in OS X. . . and some that MacKeeper did not do to boot. They were also oblivious that MacKeeper itself WAS Malware!
Anything that pitches itself as malware does (pop-ups, dialog boxes, any form of controlling navigation), should be presumed to be malware.