"The F.B.I. cast a much wider net in its terrorism investigations than it has previously acknowledged by relying on telecommunications companies to analyze phone-call patterns of the associates of Americans who had come under suspicion, according to newly obtained bureau records... The documents indicate that the Federal Bureau of Investigation used secret demands for records to obtain data not only on individuals it saw as targets but also details on their “community of interest” — the network of people that the target was in contact with.... central to a data-mining technique intelligence officials call link analysis." etc..
I've written on this before: Massive privacy violation by U.S. government and Spy Agency Mined Vast Data Trove, Officials Report - New York Times
The idea is that government spy agencies are applying data-mining techniques which is now possible with new computer technologies. In a way they're being smart and simply applying techniques already used by businesses allowing business activity to be more accurately targeted.
But with any increase in government surveillance it raises fears of intrusive government surveillance such as described by George Orwell in his book 1984. Certainly there is an example of what computer technology can do in the hands of an overzealous government. The extremely primitive not-quite-computer technology of the 1930's and 1940's, developed by IBM, was used by Nazi Germany to enact the Jewish Holocaust.
The exact issue in todays article is tracking the "envelope" information of telephone calls, and to draw a web of connections between people. When you call someone a record is made somewhere of the phone call, the number called from, the target phone number, the time of the call, and its length. This is the "envelope" and is similar to the paper envelope used to send mail through the post office. If you track enough of these phone calls you can see patterns of who is calling whom.