If you read the history of the Magic intercepts, there was a lot bad going on with those of Japanese ancestry in the U.S. during the early days of WWII, and known interaction with Japanese military/intelligence.
Magic: The Untold Story of U.S. Intelligence and the Evacuation of Japanese Residents from the West Coast During WW II
http://www.amazon.com/Magic-Intelligence-Evacuation-Japanese-Residents/dp/0960273611/ref=sr_1_9?ie=UTF8&qid=1369679011&sr=8-9&keywords=magic+intercepts
http://www.amazon.com/Magic-Intelligence-Evacuation-Japanese-Residents/dp/0960273611/ref=sr_1_9?ie=UTF8&qid=1369679011&sr=8-9&keywords=magic+intercepts ~ you might read the reviews someday. It cannot be emphasized enough that NOTHING in the Magic intercepts was ever used by any of the principals in the JA evacuation as a justification. Much of the push came from folks interested in buying up property owned by Japanese Americans at tax sales ~ one family I know of owned most of Wilshire Boulevard for much of its length from the shore to miles inland. A tempting target and sold to investors within days of their being interned.