From DreamHost’s status blog:
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.
See more on their site, although there’s very little detail about the breach itself.
Via TechCrunch.