20+ years I had some security discussions with a major exchange in the USA. In the same building were offices of Goldman Sachs and another bank (Morgan or Merril, don't remember). Anyway there was a single thinnet (10base2 ethernet) that connected them to the exchange. Yep, a quick sniff showed that everyone could see everyone else's traffic.
My contacts were genuinely surprised that this was even possible. But also I was told there would be no contract if I mentioned this to upper management in my report.
