You may have gotten an email like this, recently:

 “We’re reaching out to let you know that if you haven’t updated your Dropbox password since mid-2012, you’ll be prompted to update it the next time you sign in. This is purely a preventative measure, and we’re sorry for the inconvenience. To learn more about why we’re taking this precaution, please visit this page on our Help Center. If you have any questions, feel free to contact us at password-reset-help@dropbox.com.”

You may not get that email, but the next time you log onto dropbox, you may get a prompt to change your password.

This notification stems from a breach in 2012 where emails and salted passwords were stolen. Nice to notice this now. It links to their FAQ regarding it here: https://www.dropbox.com/help/9257?oref=e

They aren't aware of any attacks stemming from the hack, and are relating to it as a precautionary matter...for those who haven't changed passwords from mid- 2012.

Do it there and anywhere else you may have used the same email you used on dropbox, and use a unique, secure password on each site.

So...reset your password, especially if you store data there. I really hope you don't store financial/personal data anywhere online, though. It's a really bad idea to do that.

Also note that two-factor authentication SMS codes are slow or delayed, it seems.

Source:

http://www.ghacks.net/2016/08/26/dropbox-may-have-reset-your-password-just-now/