XKEYSCORE is a computer system used by the NSA to search and analyze internet data from many sources worldwide, enabling almost unlimited surveillance of anyone anywhere in the world. According to a Glenn Greenwald article in The Guardian, XKeyscore is a sort of custom search engine that allows analysts to search through vast databases containing emails, online chats and the browsing histories of millions of individuals. The data can be sorted by typing in a name, email address, or IP address, or extracted through queries, such as "My target speaks German but is in Pakistan -- how can I find him?"
One of the limitations of XKeyscore is storage. The database only has the capacity to store the massive volume of the data it collects for a few days, so essentially the XKeyscore system is best used for real time tracking of targets. In that short time frame, however, it seems to provide a very accurate digital fingerprint of any designated target in the world.
3 applications of color, with blind emboss
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