It just needs an employee who ended his employment in a way that was not to his or her liking. This is a huge risk for the company, the fines are substantial and huge companies will have a hard time keeping everything watertight and secret. Alternatively, hackers or other informed people can get to know a lot about the functioning of systems, firmware and software. So even if there is no one ratting the company out, they could still end up with those huge fines, or worse.