SAN FRANCISCO — The recent revelation that the National Security Agency was able to eavesdrop on the communications of Google and Yahoo users without breaking into either company’s data centers sounded like something pulled from a Robert Ludlum spy thriller.
How on earth, the companies asked, did the N.S.A. get their data without their knowing about it?
The most likely answer is a modern spin on a century-old eavesdropping tradition.
People knowledgeable about Google and Yahoo’s infrastructure say they believe that government spies bypassed the big Internet companies and hit them at a weak spot — the fiber-optic cables that connect data centers around the world and are owned by companies like Verizon Communications, the BT Group, the Vodafone Group and Level 3 Communications. In particular, fingers have been pointed at Level 3, the world’s largest so-called Internet backbone provider, whose cables are used by Google and Yahoo.