MacKeeper
But the real problems with MacKeeper that I can see is that it provides questionable value to most users, can destabilize an otherwise stable Mac, and embeds itself so thoroughly into the operating system that removing it is an uncomfortable and weird process.
Update (2015-05-06): Jeremy Kirk:
MacKeeper, a utility and security program for Apple computers, celebrated its fifth birthday in April. But its gift to U.S. consumers who bought the application may be a slice of a $2 million class-action settlement.
Update (2015-05-09): Thomas Reed:
In non-tech-speak, a hacker can create a link that will, if clicked, result in MacKeeper executing code embedded within the link! Such code could do things like wiping your hard drive clean, uploading data to a remote server, or downloading and installing malware.
Update (2015-08-21): Shawn King:
Half a million US customers are eligible to get at least some money back. If you know anyone who bought this crapware, please let them know about this settlement.
