Either the Rails wiki has been hacked or someone internal wanted easier access to porn.
http://wiki.rubyonrails.org/rails/
If you inspect the action of the search form on this page, you will see that it now sends anyone who wishes to use the search form, to a porn site.
Now it seems as though the wiki has been taken down. Likely to resolve this.
Hmm, the wiki is still up and still redirecting searches. For some reason, if you take the slash off the end of the URL you can still get there: http://wiki.rubyonrails.org/rails
It's been like this at least since the beginning of the week.