I haven’t got too much of a clue what this all means, but some of the MediaWiki Extensions (here, here, and here) that I have pointed to in recent posts now have a warning on them. So if you have your wiki wide open (where anyone can edit), you are apparently vulnerable to this type of attack. The UMW New Media Wiki is locked down so that only “sysops” can edit pages. I’ve been in contact with Jim Wilson, and he clearly knows way more about this stuff than I do. He has his own YouTube Extension that I have not tested, yet.