The equipment that technician Mark Klein learned was installed in the National Security Agency's "secret room" inside AT&T's San Francisco switching office isn't some sinister Big Brother box designed solely to help governments eavesdrop on citizens' internet communications. Rather, it's a powerful commercial network-analysis product with all sorts of valuable uses for network operators. It just happens to be capable of doing things that make it one of the best internet spy tools around.

"Anything that comes through (an internet protocol network), we can record," says Steve Bannerman, marketing vice president of Narus, a Mountain View, California, company. "We can reconstruct all of their e-mails along with attachments, see what web pages they clicked on, we can reconstruct their (voice over internet protocol) calls." Narus' product, the Semantic Traffic Analyzer, is a software application that runs on standard IBM or Dell servers using the Linux operating system. It's renowned within certain circles for its ability to inspect traffic in real time on high-bandwidth pipes, identifying packets of interest as they race by at up to 10 Gbps.

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