They walk among us.

Britain’s Doomsday Nuke Subs Still Run Windows XP

• Shhh! They’re watching us. Over there. Don’t look! Bloody amateur. Listen, I’m leaving now. Wait nine minutes and follow me out. Make three right turns around the block to see if you’re being tailed, then head to the park, by the carousel. Ask the vendor for a blue cotton candy “with extra gravy.” In the paper cone, you will find the answer to your question, which will be: Nobody knows for sure, but educated estimators put the number in the low thousands.

Government agencies, including the FBI, CIA, and NSA, declined to hazard a guess, or, indeed, to offer any comment at all. But figure it thusly: There are many different types of “spies” working to ferret out our secrets. Most common are your garden-variety intelligence officers posted to embassies and consulates around the country. These folks usually have some BS “official cover” like “Assistant Minister for the Promotion of Shrubbery.” “They do that job enough to maintain the cover,” says Steve Bucci, a research fellow at The Heritage Foundation, a political think tank, and a former Army Special Forces officer and Pentagon official. “The rest of their time they spend wandering around Washington, D.C., trying to make contact with people who they can then get to share information.”

Consider that 177 nations maintain a diplomatic presence here and the numbers start to add up. “The U.S. has interests all over the world, and therefore countries all over the world are interested in us. So even a small embassy will have an intelligence officer there,” says Peter Earnest, a 35-year CIA veteran and executive director of the International Spy Museum in Washington, D.C. That includes our allies, by the way. “Friends spy on friends,” says Bucci. “So Britain, Germany, every other close ally also has operatives here.”

Next, tack on what are known as NOCs (for “non-official cover”). These are professional spies posing as businessmen, journalists, students, etc. It’s “impossible to get any count on those,” says Mark Stout, a former CIA officer who heads the intelligence graduate program at Johns Hopkins University. “But you can assume at least a handful are coming in and out of the country every day.” There are also untold numbers of “co-optees,” private citizens of foreign countries who spend time in the United States under their real identities and pursue real careers, but sniff around and report any interesting findings back to their native intelligence services (or industrial competitors) as a sneaky side gig.

Far rarer are the “sleeper cell” types, like those on The Americans. But they do exist—the U.S. rounded up ten deep-cover Russian “illegals,” as they’re also known, in 2010. Stout says these spies have fake identities, life stories, and even ethnicities. One of the Russians caught in 2010—a KGB general—was posing as a Peruvian who had grown up in Uruguay. Plants are difficult and time-consuming to establish, so overall numbers are thought to be low.

Finally, we’d be remiss not to mention a fifth spy type: the traitorous American. Sadly, you’ve got to assume there are a few of these out there. “Historically, in any given year there is usually a small handful, from a couple to eight or ten, that ex post facto we find out were spying but we didn’t know at the time,” says Stout. Take all the above species of spy together, he says (and our other experts agree), “and you’re probably in the low thousands. That’s a very back-of-the-envelope guess, but I think quite low thousands is about right.”

THE MOST INTERESTING STUFF AT THE INTERNATIONAL SPY MUSEUM

1. A lipstick pistol, circa 1965, was used by KGB operatives and could fire a single shot. It was nicknamed “the kiss of death.”

2. A pigeon camera, circa World War I, was attached to a bird and took continuous photos as it flew over enemy camps. The original drone.

3. A shoe microphone and transmitter, circa 1960 to ’70, were once covertly put in the shoe of an American diplomat by Romanian spies so they could eavesdrop on his conversations.