I am not sure how it happened, but somebody (or some robot) managed to insert some malicious code into my wiki. Random people were receiving emails with links to URLs within the wiki and when they followed the links, they were redirected to malicious pages.
The URLs within the wiki resembled these:
I removed the whole Labelled_overview.png folder, which it shouldn’t have been possible for a wiki user to upload, given that I had my wiki set up to only allow logged-in users to make edits. In addition to removing the folder, I have also updated MediaWiki to the newest version. I have also set up DreamHost’s system for automatically updating MediaWiki when new versions are released, though that risks breaking extensions that are not compatible with the new software and possibly causing other problems.
I still don’t know how the malware got introduced (perhaps through a vulnerability in an old version of MediaWiki or one of my extensions), so I am keeping the whole wiki inaccessible for now.
My apologies to anyone who followed one of the malicious links.
The whole incident shows one of the annoying things about the internet. Whenever you set up a content management system like WordPress or MediaWiki, you have to be aware that there will be efforts to compromise it. As such, you need to keep it well-updated and keep an eye out for malicious activity. You can’t just set it up and forget about it.