I have just started reading a new book “The Folk Singers& The Bureau” by Aaron J.Leonard” and think there might be a lot of Mudcatters who would find it as interesting and informative as I do . As the publishers say, it is “ The first book to document the efforts of the FBI against the most famous American folk singers of the mid-twentieth century, including Woody Guthrie, 'Sis Cunningham, Pete Seeger, Lee Hays and Burl Ives. Here is a link to a podcast in which Aaron J. Leonard is interviewed about the book
https://www.youtube.com/watch?v=o658-HQuMAY&feature=emb_title