in Smithsonian about a CIA spy who tried to blackmail the USA:
Because Groat’s work was so sensitive, he had to conceal it. Although his wife understood the nature of his work, for years his children did not. “I didn’t know where my father worked until I was in high school, in the ninth or tenth grade,” says Groat's son, Shawn. “My sister typed a report on special paper that dissolved in water, although we didn’t know it. My father realized what she was doing and said, ‘You can’t use that paper.’ Then he ate the paper.