Which 20th Century US president was so obsessed with secrecy that he wrote "Burn this" on personal letters?

Lyndon Baines Johnson was so obsessed with secrecy that he often wrote "burn this" on personal letters. This was so personal that no one on Earth including me knew about this.

That's him, Tree! But don't ask me how I knew.

"The major problem in writing about Lyndon Johnson's early life was his desire for secrecy and concealment. He had a unique talent for it."
"I don't think many people would have gone to the trouble, as he did, of having pages of his college yearbook, which detailed unsavory episodes in his college career, cut out with a razor blade from hundreds of copies of the yearbook."
"A young man who worked for him when he was secretary to a congressman had been one of his students when Johnson was a high school teacher, and this man told me that after Johnson went to Washington he would write him the normal letters that a teacher writes back to the kids he has been teaching, but on each letter Johnson would write, "Burn this!"
- www.randomhouse.com