Comment Re:Just read through the PDF (Score 4, Informative) 88
They do mention a compromised domain controller, which suggests (though doesn't guarantee) Windows.
They also mention DOT, which I believe is heavily into Windows.
In the late 1980s I know there was some UNIX/X11 development going on for ATC in Germany, but I never heard whether it went big time in Europe, much less in the USA.
There are some references on the net from 2007 or so that the FAA was switching from Win to Lin, but I'm not sure what systems those were, or if it really happened. They could easily run a mix of UNIX, Linux, Windows and others on the back end, and mostly Windows on the front end.
Finally, the ATC systems probably run RTOS or a real-time UNIX.