Oh, Yes! In a previous job we developed VoIP servers (pbxes). One day a customer started experiencing some really weird problems and I was asked to debug it. I

Oh, Yes! In a previous job we developed VoIP servers (pbxes). One day a customer started experiencing some really weird problems and I was asked to debug it. I logged into the server and started analyzing traffic, turned out that traffic on a upstream VoIP switch didn't always match the traffic leaving the server I was debugging. It was as if a identical system was getting and responding to parts of the traffic. - and after some more debugging I discovered that there was a older identical system online somewhere in their server room. Years ago - all services had been stopped, the system backed up and migrated to a new server. One day there had been a power loss, and when the servers rebooted, the old system everyone had forgotten about launched it's previously stopped services - causing the customer all sorts of weird VoIP problems.