I have been trying to figure out how, logistically, large corporations focused on one huge product (like Google, Facebook, Twitter, Yahoo, etc.) restrict the information known to employees such that no single employee (or small group of employees) poses a major security threat to the company upon termination. Below, a more formal introduction.
In online applications, there is often a need for security, and obscurity. I don't know of any large companies focused on a single huge online product that openly publish the internal workings of their applications. Of course, the employees of the company must know how things work behind the curtain, in order to maintain and grow the product. But doesn't that make them an incredible security risk?
In a company of this type with tens, hundreds, or thousands of employees, it would seem any reasonably high-level employee would have the power, if he wished, to bring down the company through his knowledge of the inner mechanics of the service. The one way to prevent this would be to limit what each employee knows to what he needs to do his job. Except that then a group of one or two employees would still be able to bring down the company. What keeps a security specialist fired from Google from deciding to destroy the company, using the vulnerabilities of the very system he designed? No amount of litigation would make up for hundreds of billions of dollars in damage. Even something as seemingly simple as how the servers are connected to each other could be incredibly valuable to a hacker, and yet would really need to be shared in its entirety with employees managing the datacenters if they are to do their jobs. Some pieces of information so basic that they must be known to one person harbor incredible risk to the company if misused.
How do these companies (like Google, Facebook, Twitter, Yahoo...) restrict what each employee knows, and divide it up in sufficiently small chunks to mitigate this risk?
I'm not asking about software security, so much as how a company restricts information known to individual employees from a strategic and logistical standpoint. This same problem in different forms applies to basically any company with secrets, i.e. any company, but it is particularly important when there is one large product, especially if it's an online application, as asked above.