At the same time, though, foreigners are discouraged from studying certain topics. The security engineering group at my school lost a student a few years ago,

At the same time, though, foreigners are discouraged from studying certain topics. The security engineering group at my school lost a student a few years ago, because he was Chinese and the US government would not allow him to reenter the country due to his thesis topic (computer security). It took an assurance from the school that he would not be permitted to do any further work with his adviser and that he would switch research topics for him to be permitted entry to this country. The incredible stupidity here is that there is no classified research done by that group, nor by my own research group (cryptography). Everything is published in publicly available conferences and journals.