President Bush's chief of staff is telling the heads of all government agencies to remove such details from Web sites and public documents.
White House Chief of Staff Andrew Card requested an "immediate re-examination" of all public documents that critics said could result in the government withdrawing thousands of papers, records and reports that have been available for years. He specifically mentioned information about where nuclear materials are stockpiled.
"Government information, regardless of its age, that could reasonably be expected to assist in the development or use of weapons of mass destruction ... should not be disclosed inappropriately," Card wrote.
The heads of all agencies and executive departments "have an obligation to safeguard government records regarding weapons of mass destruction," the memo said. It gave them 90 days to report their findings to Homeland Security Director Tom Ridge.
White House spokesman Ari Fleischer defended the move in the aftermath of the Sept. 11 attacks, calling it "balanced and principled." He said agencies would have to be even more careful now and expressed hope that the private sector would follow suit.
Fleischer described the Internet as "a wonderful device" but also called it a "Catch-22."
"The Web makes it very easy for security officials to have the information. That's the upside," he said. "The bad side is that same information can be used by would-be attackers."
He told reporters government agencies, as well as private groups, had posted certain information on their Web sites that should be re-evaluated in light of the attacks on America and their aftermath. "They need to take a second look at this."
He listed examples of public and private Web sites that have been edited or taken off the Internet altogether, including how to make better explosives, poison water, or plan a germ factory.
"The world is a very different place after Sept. 11 and nobody wants to give our enemies information that can be used against us," Fleischer said.
In addition to documents on weapons of mass destruction, the White House ordered review includes "sensitive but unclassified information" that "could be misused to harm the security of our nation and the safety of our people."
An accompanying memo from the acting director of information security oversight, Laura Kimberly, told agencies and departments to classify information regardless of age that "could reasonably be expected to assist in the development or use of weapons of mass destruction."
Some of the information is non-classified and has been available to the public for years.
Steven Aftergood, who directs a government secrecy project at the Federation of American Scientists, said one "potentially troublesome feature" of the order is that the material to be reviewed includes "Sensitive But Unclassified Information."
"The need to protect such sensitive information from inappropriate disclosure should be carefully considered, on a case-by-case basis, together with the benefits that result from the open and efficient exchange of scientific, technical, and like information," according to a more-detailed memo about the directive written by the administration's Information Security Oversight Office.
But no detailed criteria for conducting such case-by-case consideration was provided, leaving this category seemingly open-ended, Aftergood said.
Fleischer acknowledged that the changes would make things more difficult for people who want the information for legitimate purposes, but said the seriousness of the threat requires caution.