DreamHost's status page shows an active incident affecting the File Manager (files.dreamhost.com) and Webmail since Oct 23. By Oct 24 it had reset passwords for affected mail and FTP/SFTP users, and by Oct 25, 9:32 PM PDT it said all affected account owners had been emailed reset instructions. Those users can't sign in until the account owner sets a new password in panel.dreamhost.com. The File Manager is still down.

DreamHost hasn't said what happened, how many accounts are affected, or whether mail or files were accessed. BleepingComputer reports that its customer notices also tell owners to check every mailbox for forwarding rules they don't recognize, which suggests some mailboxes may have been tampered with, and to change the old password wherever it was reused.

If you host there: set new passwords from the panel (don't follow emailed links; DreamHost says it will never ask for your password), remove unknown forwarders and filters, check SFTP users and recent file changes on your sites, and tell your mailbox users by phone or text, since DreamHost says it can't contact them directly.