content: Someone who possesses a TS-SCI security clearance with the US government can work for a foreign company or government if they wanted to.  Their clearance will probably be revoked and they will likely be prosecuted if they are found to have leaked classified government information; but there is no legal barrier keeping them from working wherever they want.    If Apple and Google didn't want their trade secrets from getting leaked out, they should make their employees sign non-disclosure agreements and prepare legal to sue the living pants off them if they break them.  Conspiring to not hiring their counterpart's employees is illegal and unethical.  Compartmentalization of sensitive company information should not be a justification for collusion when even the national security establishment doesn't go as far as Apple does in limiting their employee's job searching prospects.