You're new here it seems. If you want to bring something about your site to the attention to people who work at DreamHost, you are going to want to file a Support ticket by logging into the Web Panel. That way you can tell them how much you know and what your site is so they can actually "look into the issue."
Other than that in addition to changing passwords you're going to want to run antivirus/anti-malware software on all computers used to update the site or may have accessed the web panel. There maybe a keylogger stealing your passwords and if that is the case just changing them won't prevent this from occurring again. Also don't forgot to get yourself an education in net security by researching the subject or seeking the services of someone with expertise.
Customer since 2000 openvein.org