A slide from an NSA briefing, courtesy of Edward Snowden.

Then, an explanation from the Washington Post.

The operation to infiltrate data links exploits a fundamental weakness in systems architecture. To guard against data loss and system slowdowns, Google and Yahoo maintain fortresslike data centers across four continents and connect them with thousands of miles of fiber-optic cable. Data move seamlessly around these globe-spanning “cloud” networks, which represent billions of dollars of investment.

For the data centers to operate effectively, they synchronize large volumes of information about account holders. Yahoo’s internal network, for example, sometimes transmits entire e-mail archives — years of messages and attachments — from one data center to another.

Tapping the Google and Yahoo clouds allows the NSA to intercept communications in real time and to take “a retrospective look at target activity,” according to one internal NSA document.

Note the smiley under the dotted arrow pointing at the GFE interface.

So, remind me again: why would you trust an American Internet company?