> I mean are the people that operate daily these machines vetted to a level where you can totally exclude that they (in ALL airports wordwide) can be affiliated to whatever evil organization and do some tests after hours?
No, although after-hours testing may set off some alarms. I'm sure their on-hours experience would be useful, though.
> Does the same happen for all technicians that maintain/repair these devices?
No.
> Does the same happen for all designers of these devices?
Nope.
> Or if you prefer, do you believe that such a scanning machine cannot be re-built from commercial parts by someone who knows their innards?
Yes, I do believe that rebuilding a modern, advanced x-ray system from scrap components is beyond the capabilities of ISIS at the moment.
> Are ALL purchases of new scanners subject to governemnet approval (and even if yes, which government)?
The modern, advanced x-ray systems are not available to the general public. As to how exactly they are controlled, I'm not sure.
See also my comments to other users regarding the differences between modern x-rays and old school ones.
