"Spam has proven to be a significant problem for the NSA — clogging databases with information that holds no foreign intelligence value. The majority of all e-mails, one NSA document says, “are SPAM from ‘fake’ addresses and never ‘delivered’ to targets.”
"In fall 2011, according to an NSA presentation, the Yahoo account of an Iranian target was “hacked by an unknown actor,” who used it to send spam. The Iranian had “a number of Yahoo groups in his/her contact list, some with many hundreds or thousands of members.”
"The cascading effects of repeated spam messages, compounded by the automatic addition of the Iranian’s contacts to other people’s address books, led to a massive spike in the volume of traffic collected by the Australian intelligence service on the NSA’s behalf.
"After nine days of data-bombing, the Iranian’s contact book and contact books for several people within it were “emergency detasked.”"
The report is headlined "NSA collects millions of e-mail address books globally". That's "globally" as in technically anywhere outside the United States, and "millions" as in 250 million per year:
"During a single day last year, the NSA’s Special Source Operations branch collected 444,743 e-mail address books from Yahoo, 105,068 from Hotmail, 82,857 from Facebook, 33,697 from Gmail and 22,881 from unspecified other providers, according to an internal NSA PowerPoint presentation. Those figures, described as a typical daily intake in the document, correspond to a rate of more than 250 million a year."