Honestly still today, for some critial jobs, I do not understand companies not hiring local people (whatever nationality) with their friends and whole family (parents, cousins, etc) in the country. The cost of treason is higher (if they need to escape the country). It is not bullet proof, but it mitigates the risk.
But it looks like banks have a short memory (This guy was a sysadmin): https://en.wikipedia.org/wiki/Herv%C3%A9_Falciani