Many news souces are quoting that nearly 7 million users of Dropbox may have been compromised world-wide, but Dropbox says:
"Recent news articles claiming that Dropbox was hacked aren’t true. Your stuff is safe. The usernames and passwords referenced in these articles were stolen from unrelated services, not Dropbox. Attackers then used these stolen credentials to try to log in to sites across the internet, including Dropbox. We have measures in place to detect suspicious login activity and we automatically reset passwords when it happens.
Attacks like these are one of the reasons why we strongly encourage users not to reuse passwords across services. For an added layer of security, we always recommend enabling 2 step verification on your account.
Update: 10/14/2014 12:30am PT
A subsequent list of usernames and passwords has been posted online. We’ve checked and these are not associated with Dropbox accounts."
Seems like good advice to change your Dropbox credentials anyway, and to enable the 2 step verification process.