Back in April 2004, the ACLU brought a case against the United States government in which they argued that the FBI had no right to demand sensitive customer information from an unnamed internet company. In the case, the FBI had claimed that the Patriot Act expressly gave the agency this power, and moreover, that it could prevent the internet company from even informing its customers of the info handover. Eventually, a New York judge, Victor Marrero, declared this portion of the Patriot Act unconstitutional, and ruled against the FBI.
As mentioned, this case took place way back in April, and Judge Marrero's ruling made the headlines, but details of the case itself were placed under a gag order by the U.S. government. It was only yesterday that the ACLU released documents from the case. Apparently, the government wanted some of the documents kept from the public solely because they contained the words "sensitive," "national security," or "FBI". Even an ACLU letter to Judge Marrero objecting to the gag order was kept from the public. Looking through the documents, it's hard to find anything that appears to be "sensitive information," besides perhaps the ACLU's argument that the FBI was doing something unconstitutional.
In a related vein, the administration has also been attempting to use the "state secrets privilege" to avoid even having to defend its actions in court. It is a growing body of evidence that reveals a systematic governmental effort to obscure basic information regarding the constitutional nature of the government’s actions from the public. This is all being done in the name of national security. The legitimacy behind this censorship should certainly be called into question.