John F. Burns | London | December 2

NYT - Psst! Wanna be a spy?

Back in the cloak-and-dagger days of secret intelligence work, Britain’s espionage agencies liked to recruit in the ivied colleges of Oxford and Cambridge, even if that brought them some of the most notorious turncoats of the 20th century, men like Kim Philby and other Cambridge spies who handed atom bomb secrets to the Soviet Union in the 1940s and 1950s before defecting to Moscow.

In the Internet age, the spy catchers have been forced to go digital, democratic and, old-timers might say, outright pop. Their latest whiz, causing a buzz on the Internet — and stirring a torrent of Web chat among people identifying themselves as hackers — is an online cryptographic puzzle that promises a fast track to recruitment as spies for those who solve it before the challenge expires on Dec. 11.

According to traffic on Twitter, Facebook and scores of other Web sites, at least 50 people have solved the puzzle since it was posted unobtrusively last month. To all but practiced cryptographers, it looks baffling: a rectangular display of 160 letters and numbers, grouped in twos in blue against a black background, under the overline, “Can you crack it?” Beneath it, a digital clock ticks down the seconds left until the competition closes.

The agency that posted the puzzle at www.canyoucrackit.co.uk is one of the oldest, and, espionage experts say, most successful eavesdropping organizations anywhere, Government Communications Headquarters, or GCHQ, located in a vast doughnut-shaped building surrounded by huge satellite dishes in parkland near Cheltenham, 120 miles west of London.

Helped by a hand-in-glove relationship with its American counterpart, the National Security Agency, which provides access to data downloaded from a pervasive network of American spy satellites, GCHQ can hack into phone calls, e-mails and computers virtually anywhere in the world. With language experts speaking everything from Amharic to Kazakh and 70 tongues besides, it has played a crucial role in cracking some of the biggest terror plots against the West in recent years.