Hiring foreign nationals to work on sensitive technology is called a "deemed export" and needs an export license.
Read all about it at http://www.bxa.doc.gov.
At the same time, the government's review of export licenses has been gutted.
See http://www.freerepublic.com/forum/a3af2567722df.html.
So foreign terrorists can come and legally get training on full motion simulators, which aren't export controlled. If they were export controlled, the schools would need an export license to enroll these students.