Independent security researcher Troy Hunt has verified that Dropbox account data for 68 million user's email addresses and passwords has been leaked to the internet. From the August 31rst Guardian article "Dropbox hack leads to dumping of 68m user passwords on the internet", Hunt is quoted saying that "There is no doubt whatsoever that the data breach contains legitimate Dropbox passwords, you simply can’t fabricate this sort of thing."
The original Dropbox data breach dates back to 2012. If you have a Dropbox account and are concerned your account may be compromised, here is a link to the Dropbox support article "I think my account was compromised. What do I do?"
If you have reused your Dropbox password elsewhere on any other online services or websites, we would recommend changing passwords on the other locations as soon as possible.