What about the NYSE?

Reader Kevin French emails:

Dubai Ports World is returning the six US Ports to American control and this heads off a political showdown between the White House and the folks up on Capitol Hill but who will be next? I notice the NYSE company has just been listed on the New York Stock Exchange. I just wonder what would happen if a foreign company tried to take a controlling stake in this American financial icon? Anyway, I think any foreign company thinking of purchasing a large American firm from now until the 08 vote might reconsider it because the Democrats and Republicans will jump on it for political advantage. The question now is which American companies do not pose a threat to national security, so they maybe acquired by a non-US company?