Okay, here's the deal with MacKeeper:
Technically, MK is legitimate software. Many people and companies agree with this notion, including Apple themselves. It is NOT the same thing as MacDefender, MacProtector, etc etc, which is agreed by all to be legitimate malware. Apple considers this malware as well.
However, MacKeeper is not something one should download onto their computers for a couple of reasons:
1. MacKeeper is unnecessary. Every single task it performs can be performed by another app or built-in process for cheap or free. Moreover, some say that certain features of MK aren't needed at all, specifically, the "cache cleaning" feature. This is debatable, but cache cleaning is also available for less. I won't list all of the suggestions for alternatives, but they can be easily found.
2. MacKeeper has been said to cause problems on computers. I've seen posts all over saying that MacKeeper slows computers down, cleans necessary files off of the system, and many users have had to reinstall their systems because of MacKeeper-related problems
3. Finally, the company that started MacKeeper, ZeoBIT, is known for using marketing practices that range from annoying to unethical:
- Popunders and popovers that aren't blocked by popup blockers. These popups use very Apple-like graphics, including the Spinning Beach Ball of Doom. Also, hasn't anyone noticed that the MK logo looks a ton like Apple's Automator logo? It nearly fooled me the first time I saw it....
- ZeoBIT has been known to bribe people for positive reviews on web sites. The rewards have included free upgrades, and in one notable case, a job as a ZeoBIT consultant.
- Worst of all was the clamxav.org scam. ClamXav, for those of you who don't know, is a competing AV software. Their site is clamxav.com. ZeoBIT bought a similar site, clamxav.org, and wrote a "review" of ClamXav. And then there was a Download button, which actually redirected to the MacKeeper website. I mean, honestly...