In the world of network security, it has been generally assumed that private networks were inherently secure, so most all attention is given to securing and segregating internet facing services instead. Unfortunately this is no longer the case, while traditional security measures have been adequate for traditional intrusions, the NSA's reach is far greater than a normal hacker. Because of the technical constraints involved in tapping these private networks, it is now generally accepted that the NSA would have needed to physically intercept the fiber optic cables between Google's data centers in order to accomplish this task, in response to this intrusion, Google has begun encrypting all traffic between data centers on their private networks.
The NSA, working with its British counterpart, the Government Communications Headquarters (GCHQ), secretly taps into the internal networks of Yahoo and Google, the two biggest Internet companies by overall data traffic. The operation intercepts information flowing between the enormous data centers that those companies maintain around the world. In general, Google and Yahoo use privately owned or leased lines to synchronize their data centers. This graphic shows how the NSA and GCHQ break into those internal networks, using Google’s as an example. Less is known about Yahoo’s networks, but the NSA operations are thought to be similar.
IMAGE SOURCE: Staff reports; Google, www.google.com/about/datacenters.