Whenever Google detects a competitive app or "malicious one", they remove it from their list of apps in Play Store. My best guess is that security master is currently competing with the new Android phone master that comes pre-installed. To confirm, if you still have Security Master installed, check your list of installed apps using Play Store, you won't find any cheetah mobile apps listed (that is, Clean Master and Security Master)

I recently deleted clean master. I was trying to update and noticed it was removed from the app store. So I googled why is it gone. Come to find out that it was taking information from you. it was BANNED. Omg. I couldnt believe it, but glad I found out. so now I'm double checking in security master is safe. Because it's now no longer in the app store. But now, since the previous commenter,said that those cheetah apps were together. Then I guess I have to delete security master now. Beware