RCE via exposed JMX server on jabber.37signals.com/jabber.basecamp.com

@ian reported that `jabber.37signals.com` and `jabber.basecamp.com` exposed on port `555` an unauthenticated Java JMX server which was vulnerable to RCE. We've looked into this and found that we forgot to clean up some DNS records when we decomissioned Jabber so the exposed IP address were not part of our infrastructure. We've removed the old DNS entries for `jabber.basecamp.com` / `jabber.37signals.com`.