With every new leak from Edward Snowden’s bottomless trove of pilfered documents, it gets harder to keep track of all the bizarre ways the National Security Agency has cooked up to spy on people and governments. This may help.

Data in Motion 
NSA’s spies divide targets into two broad categories: data in motion and data at rest. Information moving to and from mobile phones, computers, data centers, and satellites is often easier to grab, and the agency sucks up vast amounts worldwide. Yet common data such as e-mail is often protected with encryption once it leaves a device, making it harder—but not impossible—to crack.

Data at Rest 
Retrieving information from hard drives, overseas data centers, or cell phones is more difficult, but it’s often more valuable because stored data is less likely to be encrypted, and spies can zero in on exactly what they want. NSA lawyers can compel U.S. companies to hand over some of it; agency hackers target the most coveted and fortified secrets inside computers of foreign governments.

Where the Data Goes 
Much of the data the NSA compiles from all these efforts will be stored in its million-square-foot data center near Bluffdale, Utah. It can hold an estimated 12 exabytes of data. An exabyte is the equivalent of 1 billion gigabytes.

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