In my earlier days I used FS2000, with an add on called Squawkbox (see
here. It is a free download
This was basically an FMS that you could load a flight plan using waypoints and navaids (VOR's, NDB's, etc). There were a number of sites where you could 'plan a route. You could then go online and 'fly with others in controlled airspace - there was a controller add on called Procontroller (also free), which functioned like a radar, interpreting the whereabouts of the sim aircraft. In the later incarnations the 'ATC' was all done in voice using Roger Wilco. I have no evidence to suggest that any terrorists used this, but I do know that the guys who controlled various sectors used the lates SID and STARS and virtual pilots were expected to adhere to these (see
here. The level of realism in that respect was amazing (even more so as they linked the weather on the flight sim to real time weather from airport ATIS servers).
However, I fully agree a PC sim is not like handling an aircraft in anyway, even with force feed controls. The difficulty lies in the limitations of a monitor[/URL]