Wild Bill Donovan would have loved the Internet. The American spymaster who built the Office of Strategic Services in World War II and later laid the roots for the CIA was obsessed with information. Donovan believed in using whatever tools came to hand in the "great game" of espionage. These days the Net, which has already remade such mundane pastimes as buying books and sending mail, is reshaping Donovan's vocation as well.
The latest revolution isn't simply a matter of gentlemen reading other gentlemen's e-mail. That kind of electronic spying has been going on for decades. In the past three or...