Halvar Flake was scheduled to teach a class on computer security entitled Analyzing Software for Security Vulnerabilities today and tomorrow at Blackhat Training in Las Vegas. Instead, US customs officials cross-examined him for nearly five hours, then decided not to allow him into the country and put him on a plane back to Germany.
This would not have been Flake's first time to teach at Blackhat Training -- in fact, it would have been his seventh year to do so. According to Flake, many of his students during the previous years have been "US government-related folks, mostly working on US National Security in some form. I have trained people from the DoD, DoE, DHS, and most other agencies that come to mind."
According to his blog entry about the affair, Flake's crime seems to have been carrying printed training material with him in his baggage. They turned up when customs searched his suitcase, and led to his interrogation.
Compounding the issue in the eyes of the feds doing the deciding was the fact that the training arrangements between Flake and Blackhat Training were not between two businesses, but between Flake personally and Blackhat. The folks at immigrations took exception to this, concluding that Flake was actually an employee of Blackhat Training, and would therefore require an H-1B visa in order to get into the country for the two days of training.