Dreamhost, one of the interwebs most popular hosting providers has recently forced a password change on all it's users account due to possible unauthorised client data access.
Dreamhost's Twitter feed excerpt;

Last night we detected some unauthorized activity within one of our databases. While we don't have evidence that customer passwords were taken at this time, we're forcing a change out of caution. Please login to our web panel and change any passwords you may have with us. We'll keep this post updated as we get more information.

Update Jan 20th, 09:50pm PST: We're going to set this post to resolved. We have been sending out update emails to every account owner we have, letting them know what happened, and how to proceed from here on out. As a precaution, we advise every user to change all email passwords as well. We are not forcing this change, however, so make sure you take care of that ASAP. -Brian H

Update Jan 20th, 08:15pm PST: Forced updates to FTP/shell users should now be done. Any users that are locked out should update their passwords via the web panel. If you're still unable to get in, please let support know asap. -Brian H