If you are an investment banker, and you settle into your seat on a train after a long day of doing investment banking, and after a while you look up from your novel and notice that the person sitting next to you is also an investment banker, a competitor, and not only that but he is doing investment banking right now, and not only that but you can see his email and figure out what company he is working for and what deal he is working on, what should you do?
There is a correct answer, and you are not going to like it, but it is: You should get out your phone and, carefully and casually and without letting him see your screen, you should email the people back at your office and try to get them to pitch his client right now and take the deal away from him, or at least get a role in it. Then your colleagues will scramble to use the information you gather to put together, within the hour, a compelling pitch to the client, and they will call the client and present their credentials and make their pitch, and the client will say "wait how did you even know we were doing a deal, it is secret," and your colleagues will smugly reply "we are investment bankers, it is our business to know what deals are going on, and we are very good at our business, also by the way if I were you I'd have some questions for your current bankers about leaks," and the client will be impressed and hire your bank and fire the other guy's bank.
Comment: Also see: What's occurring at Fukushima since the meltdown in 2011