"In the weeks after the Sept. 11, 2001, attacks, FBI agents armed with warrants made visits to the Paterson, N.J., Public Library and took away two computers provided for the public. They apparently hoped to scan the hard drives for clues to the activities of three hijackers with ties to the city."
"The incident made few headlines, but it turned out to be the tip of a domestic surveillance iceberg. Last June, a University of Illinois survey said local or federal authorities had asked 85 libraries across the country for information about patrons."
"That the survey found so many is a surprise: The USA Patriot Act, passed in October 2001, made it illegal for librarians to tell anyone about FBI library raids." (from Law.com)