applehelpwriter:

If you have Dropbox installed, take a look at System Preferences > Security & Privacy > Accessibility tab. Notice something? Ever wondered how it got in there? Do you think you might have put that in there yourself after Dropbox asked you for permission to control the computer?

No, I can assure you that your memory isn’t faulty. You don’t remember doing that because Dropbox never presented this dialog to you, as it should have

There really isn’t any excuse for Dropbox to ride roughshod over users’ security and preference choices.

This is really poor security from Dropbox. As of this writing, they have not responded to this issue or offered any explanations or solutions.