Herbert Yardley and Edward Snowden highlight ironies of United States snooping history

In 1929, the US government fired a young, talented intelligence officer who institutionalised America's first permanent agency to intercept foreign messages and break into their classified information. The secretary of state at the time, Henry Stimson, was so furious when he found Herbert Yardley and his boys had been busily snooping on other countries' diplomatic telegraphs that he ordered the cipher bureau to be closed and Yardley sacked. "Gentlemen do not read each other's mail," Stimson famously said in his memoire over his decision to remove Yardley.

Shamefaced and broken, Yardley could not find another place to use his skills. To support his family, the code-breaker, in his early 30s, wrote a controversial book, The American Black Chamber, which detailed the internal operation of America's intelligence work. The book led to the amendment of the Espionage Act, which Washington used to seize all his remaining material.

Some 84 years later, another young, bright US intelligence officer, Edward Snowden, earned the wrath of the White House. Unlike Yardley, Snowden became an outcast because he could not stand the gentlemen reading others' personal mail.

Snowden did not write a book - not yet at least. Instead he chose to tell the story to the international media, gaining wide attention.

Despite falling from Washington's grace, Yardley was later hired by other governments, most notably the Chinese government to help overhaul their intelligence work. Years later, he penned another exposé, The Chinese Black Chamber, which was declassified and published in 1983. He was also inducted into the Military Intelligence Hall of Fame. Snowden, on the other hand, could face lengthy jail time if the US authorities get their hands on him.

Both Yardley and Snowden will be remembered as among the most colourful and controversial figures in American intelligence history. They shared as many similarities as differences. One thing that remains unchanged is the moral ambiguity over how much a sovereign state should be allowed to tap into others' secrets in the name of national security.