“Boy, you sure have a lot of apps on your phone.”

“Well, it’s my job.”

“What’s your favorite?”

“Oh, I love Daisy Slots, with so many casino games options, I couldn’t choose. But hey, want to see one to set your skin crawling?”

It was the flush end of a pleasurably hot day — 85 degrees in March — and we were all sipping bitter cocktails out in my friend’s backyard, which was both his smoking room, beer garden, viticetum, opossum parlor and barbecue pit. I was enjoying the warm dusk with a group of six of my best friends, all of whom seemed interested, except for my girlfriend… who immediately grimaced.

“Girls Around Me? Again?” she scolded. “Don’t show them that.”

She turned to our friends, apologetically.

“He’s become obsessed with this app. It’s creepy.”

I sputtered, I nevered, and I denied it, but it was true. I had become obsessed with Girls Around Me, an app that perfectly distills many of the most worrying issues related to social networking, privacy and the rise of the smartphone into a perfect case study that anyone can understand.

It’s an app that can be interpreted many ways. It is as innocent as it is insidious; it is just as likely to be reacted to with laughter as it is with tears; it is as much of a novelty as it has the potential to be used a tool for rapists and stalkers.

And more than anything, it’s a wake-up call about privacy.

The only way to really explain Girls Around Me to people is to load it up and show them how it works, so I did. I placed my iPhone on the table in front of everyone, and opened the app.

The splash screen elicited laughter all around. It’s such a bitmap paean to the tackiest and most self-parodying of baller “culture”; it might as well be an app Tom Haverford slapped together in Parks And Recreation. But it does, at a glance, sum up what Girls Around Me is all about: a radar overlaid on top of a Google Map, out of which throbs numerous holographic women posing like pole dancers in a perpetual state of undress.

“Okay, so here’s the way the app works,” I explained to my friends.

Girls Around Me is a standard geolocation based maps app, similar to any other app that attempts to alert you to things of interest in your immediate vicinity: whether it be parties, clubs, deals, or what have you. When you load it up, the first thing Girls Around Me does is figure out where you are and load up a Google Map centered around your location. The rest of the interface is very simple: in the top left corner, there’s a button that looks like a radar display, at the right corner, there’s a fuel meter (used to fund the app’s freemium model), and on the bottom left is a button that allows you to specify between whether you’re interested in women, men or both.

It’s when you push the radar button that Girls Around Me does what it says on the tin. I pressed the button for my friends. Immediately, Girls Around Me went into radar mode, and after just a few seconds, the map around us was filled with pictures of girls who were in the neighborhood. Since I was showing off the app on a Saturday night, there were dozens of girls out on the town in our local area.

“Wait… what? Are these girls prostitutes?” one of my friends asked, which given the Matrix-like silhouettes posing on the splash screen was a pretty good question.

“Oh, no,” I replied. “These are just regular girls. See this girl? Her name’s Zoe. She lives on the same street as me and Brittany. She works at a coffee shop, and I’m pretty sure she doesn’t moonlight picking up tricks.”

“How does it know where these girls are? Do you know all these girls? Is it plucking data from your address book or something?” another friend asked.

“Not at all. These are all girls with publicly visible Facebook profiles who have checked into these locations recently using Foursquare. Girls Around Me then shows you a map where all the girls in your area trackable by Foursquare area. If there’s more than one girl at a location, you see the number of girls there in a red bubble. Click on that, and you can see pictures of all the girls who are at that location at any given time. The pictures you are seeing are their social network profile pictures.”

“Okay, so they know that their data can be used like this for anyone to see? They’re okay with it? ”

“Probably not, actually. The settings determining how visible your Facebook and Foursquare data is are complicated, and tend to be meaningless to people who don’t really understand issues about privacy,” I explained. “Most privacy settings on social networks default to share everything with everyone, and since most people never change those… well, they end up getting sucked up into apps like this.”

“But they know they’ve checked in, right?”

“Again, not necessarily. Foursquare lets you check other people into a location. If you get checked into Foursquare by a friend without your knowledge and have a publicly visible Facebook profile, you could end up in here.” (Update: Apparently, I wasn’t correct about this. Foursquare does NOT allow you to check other people in with you without their knowledge; I was confusing Foursquare for Facebook, which does offer this functionality. Thanks for the correction, unknown8bit! – JRB)

One of my less computer-affable friends actually went pale, and kept on shooting her boyfriend looks for assurance. A Linux aficionado who was the only person in our group without a Facebook account (and one of the few people I’d ever met who actually endorsed Diaspora), the look he returned was one of comical smugness.

“But wait! It gets worse!” I said, ramping things up.

“So let’s say I’m a bro, looking to go out for a night on the town and pick someone up. Let’s say I’m going to the Independent around the corner, and checking it out ahead of time, I really like the look of this girl Zoe — she looks like a girl I might want to try to get with tonight — so I tap her picture for more information, see what I can find out about here.”

I tapped on Zoe. Girls Around Me quickly loaded up a fullscreen render of her Facebook profile picture. The app then told me where Zoe had last been seen (The Independent) and when (15 minutes ago). A big green button at the bottom reading “Photos & Messaging” just begged to be tapped, and when I did, I was whisked away to Zoe’s Facebook profile.

“Okay, so here’s Zoe. Most of her information is visible, so I now know her full name. I can see at a glance that she’s single, that she is 24, that she went to Stoneham High School and Bunker Hill Community College, that she likes to travel, that her favorite book is Gone With The Wind and her favorite musician is Tori Amos, and that she’s a liberal. I can see the names of her family and friends. I can see her birthday.”

“All of that is visible on Facebook?” one of the other girls in our group asked.

“More, depending on how your privacy settings are configured! For example, I can also look at Zoe’s pictures.”

I tapped on the photo album, and a collection of hundreds of publicly visible photos loaded up. I quickly browsed them.

“Okay, so it looks like Zoe is my kind of girl. From her photo albums, I can see that she likes to party, and given the number of guys she takes photos with at bars and clubs at night, I can deduce that she’s frisky when she’s drunk, and her favorite drink is a frosty margarita. She appears to have recently been in Rome. Also, since her photo album contains pictures she took at the beach, I now know what Zoe looks like in a bikini… which, as it happens, is pretty damn good.”

My girlfriend scowled at me. I assured her Zoe in a bikini was no comparison, and moved on.

“So now I know everything to know about Zoe. I know where she is. I know what she looks like, both clothed and mostly disrobed. I know her full name, her parents’ full names, her brother’s full name. I know what she likes to drink. I know where she went to school. I know what she likes and dislikes. All I need to do now is go down to the Independent, ask her if she remembers me from Stoneham High, ask her how her brother Mike is doing, buy her a frosty margarita, and start waxing eloquently about that beautiful summer I spent in Roma.”

Throughout this demonstration, my group of friends had been split pretty evenly along gender lines in their reactions. Across the board, the men either looked amused or (in the case of my beardo Diaspora friend) philosophically pleased with themselves about their existing opinions about social networking. The women, on the other hand, looked sick and horrified.

It was at this point, though, that the tendrils of the girls’ unease — their deeply empathic sense of someone being unsafe — seemed to creep through the entire group.

“And if that doesn’t work on Zoe,” I concluded, consulting the app one last time. “There are — let’s see — nine other girls at the Independent tonight.”

Often times, a writer uses tricks and exaggerations to convey to a reader the spirit — if not the precise truth — of what occurred. I just want to make clear that when I say that one of my friends was actually on the verge of tears, you understand that this is not such a trick. She was horrified to the point of crying.

“How can Apple let people download an app like this?” she asked. “And have you written about this?”

In answer to the first question, I replied that as sleazy as this app seemed, Girls Around Me wasn’t actually doing anything wrong. Sure, on the surface, it looks like a hook-up app like Grindr for potential stalkers and date rapists, but all that Girls Around Me is really doing is using public APIs from Google Maps, Facebook and Foursquare and mashing them all up together, so you could see who had checked-in at locations in your area, and learn more about them. Moreover, the girls (and men!) shown in Girls Around Me all had the power to opt out of this information being visible to strangers, but whether out of ignorance, apathy or laziness, they had all neglected to do so. This was all public information. Nothing Girls Around Me does violates any of Apple’s policies.

In fact, Girls Around Me wasn’t even the real problem.

“It’s not, really, that we’re all horrified by what this app does, is it?” I asked, finishing my drink. “It’s that we’re all horrified by how exposed these girls are, and how exposed services like Facebook and Foursquare let them be without their knowledge.”

But I didn’t have an easy answer ready for my friend’s last question. I’d been playing with the app for almost two months. Why hadn’t I written about it? None of the answers made me look good.

Part of it was because, like many tech professionals, I had taken for granted that people understood that their Facebook profiles and Foursquare data were publicly visible unless they explicitly said otherwise… and like my beardo Diaspora friend, I secretly believed that people who were exposed this way on the Internet without their knowledge were foolish.

That made Girls Around Me a funny curio, a titillating novelty app, the kind of thing you pulled out with your buddies at the bar to laugh about… and maybe secretly wish had been around when you were younger and single and trying to pull some action. And if I’d written a post about it a month ago, it would have probably been from that angle. The headline might well have been: “No More Sausage Fests With Girls Around Me [Humor]”

It was in just this spirit that I’d shown off the app to my friends in the first place. It was getting late, we were all drunk or on the verge of getting there, and it had been a perfect day. It would have been so nice to finish things with a laugh. But now, as six intelligent, sophisticated friends from a variety of backgrounds surrounded me — some looking sick, some looking angry, and some with genuine fear in their faces — I didn’t think Girls Around Me was so funny. It had cast a pall across a beautiful day, and it had made people I loved feel scared… not just for the people they loved, but for complete strangers.

So I’m writing about it now. Not because Girls Around Me is an evil app that should be pulled from the iOS App Store, or because the company that makes it — Moscow-based i-Free — is filled with villains. I still don’t believe that there’s anything wrong with what this app is doing, and the guys at i-Free are super nice, and certainly don’t mean for this app to be anything beyond a diversion. So, the reason I’m writing about Girls Around Me is because I finally know what to say about it, and what it means in the greater picture.

Girls Around Me isn’t an app you should use to pick up girls, or guys for that matter. This is an app you should download to teach the people you care about that privacy issues are real, that social networks like Facebook and Foursquare expose you and the ones you love, and that if you do not know exactly how much you are sharing, you are as easily preyed upon as if you were naked. I can think of no better way to get a person to realize that they should understand their Facebook privacy settings then pulling out this app.

That’s why I hope you’ll go download Girls Around Me on your iPhone or iPad. It’s free to download. Show it to someone. Give them the same demo I gave to my friends. Then, when they ask how it’s done and how they can prevent an app like Girls Around Me from tracking them, educate them about privacy.

Here’s a good place to start.

Update: In response to this story, Foursquare has killed Girls Around Me’s API access to their data, effectively knocking the app out of commission. For more details and a statement from Foursquare, read here.

Update 2: As of Saturday evening, Girls Around Me has been yanked from the iOS App Store.

Update 3: Girls Around Me developer i-Free has released a full statement on the app, in which they say they’ve done nothing wrong and been made a scapegoat for privacy issues. You can read their response — and ours — here.

Update 4: Think this issue’s dead now that Girls Around Me has been killed? It’s not at all. In fact, it’s very possible Girls Around Me could come back with its core functionality intact.

Update 5: We’ve written a guide on cutting apps like Foursquare and Facebook off from tracking your data. Read it here.

Update 6: Girls Around Me’s developer gave Cult of Mac an interview, in which they said that the app wasn’t for stalking girls without their knowledge, but for avoiding women who are ugly.