Margo Anderson and William Seltzer have found evidence that the U.S. Census Bureau handed over the names and addresses of Japanese-Americans living in and around Washington, D.C., to the Secret Service during World War II. The release occurred after Congress suspended the Bureau's legally mandated protection of confidentiality in 1942.
Anderson and Seltzer discovered in 2000 that the Census Bureau released block-by-block data during WW II that alerted officials to neighborhoods in California, Arizona, Wyoming, Colorado, Utah, Idaho and Arkansas where Japanese-Americans were living. "We had suggestive but not very conclusive evidence that they had also provided microdata for surveillance," Anderson says.
Anderson says that microdata would have been useful for what officials called the "mopping up" of potential Japanese-Americans who had eluded internment. [Link]