"Mills received numerous messages of support and appreciation of his book. He was also criticized, insulted and threatened. According to the FBI, a few days following the appearance of Listen, Yankee, someone sent Mills an anonymous letter warning him that "an American agent disguised as a South American would assassinate him on his next visit to Cuba." In a memo dated November 29, 1960, the FBI noted that "Mills indicated he would not be surprised if this were true since he does not doubt that the Federal Bureau of Investigation and other similar United States organizations do not approve of his activities. Mills has made several inquiries in regard to purchasing a gun for self-protection." It is significant that the paragraph immediately following this quote is blacked out by the FBI and remains classified."