The agency applies a series of filters to the data it intercepts to reduce the volumes. For instance, the first filter throws out all high-volume, low-value traffic such as peer-to-peer downloads, reducing traffic volumes by up to 30% right away, the paper noted.
Numerous other filters pull out information that is of specific interest to the NSA or GCHQ. The NSA uses a total of 31,000 specific search terms, including specific phone numbers, email addresses and other identifiers to keep an eye on communications being carried out by persons or entities of interest. The GCHQ uses about 40,000 such terms to filter the information it intercepts.
The technology allows GCHQ to store certain information of interest for up to three days and phone call metadata for up to 30 days. Such data interception and filtering has apparently allowed the agency to identify potential terrorist threats, child exploitation networks and cyber threats.
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