I’ve told you many times (here, here, here, here, and here) that if you’re using Dropbox and you have any file in it that you wouldn’t like to see on the Internet, then you better be encrypting those files. Dropbox is a great product and their developers take care to make it as secure as possible but bugs still creep in. If you’re a developer, that knowledge is held in your DNA. If you’re not a developer, take my word for it: bugs always creep in.
Now it’s Dropbox’s turn. The problem occurs when users issue a shared link. That can result in an unintentional file leak. Dropbox has disabled the shared link mechanism while they consider ways of tightening things up. The problem results not from a flaw but from the fact that the links can be revealed in unexpected ways—see the article for the details.
So here’s the bottom line: if you’re going to issue a shared link you should require a password and/or expire it after a set time. If there’s anything really sensitive in the file set being shared, you had better encrypt it. Yes, it’s a pain for your collaborators but it’s better than having your secret plans for world domination revealed.