Mike Cerre:

Once inside, hackers can disrupt a network's operations, like they did last year to the British Health System, forcing hospitals to down. Or they can steal confidential information, like Equifax's credit reports on more than 145 million Americans.

So far, the most serious cyber-security breaches of U.S. defense and intelligence networks were inside jobs. Army PFC Bradley Manning, who now identifies as Chelsea, copied and released nearly a million classified documents.

The leaking of the NSA's surveillance techniques and other classified material by a subcontractor, Edward Snowden. There are also accidental security breaches, like the careless use of a flash drive by a military unit in the Middle East in 2008 that temporarily created an opening into the Defense Department's network.

These cyber-teams are drawn from all the services and ranks. Some were trained by the military. Others were recruited for their cyber-skills.