Prior to this, some have assumed that Dropbox was hacked, which is how the hackers have managed to get their hands on these usernames and passwords. Well the good news is that Dropbox has not been hacked, at least according to a statement released by the company who refuted the hacking claims.
According to Dropbox, “These usernames and passwords were unfortunately stolen from other services and used in attempts to log in to Dropbox accounts. We’d previously detected these attacks and the vast majority of the passwords posted have been expired for some time now. All other remaining passwords have been expired as well.”
In the meantime while it is unclear if your Dropbox account might have been compromised, it might still be a good idea for you to go ahead and change your Dropbox password, especially if you have not done it in a while, just to err on the side of caution.