One essential aspect of privacy is the ability to control how much we disclose to others. Unfortunately, we’ve lost much of that control now that every photo, chat, or status update posted on a social-media site can be stored in the cloud: even though we intended to share that information with someone, we don’t necessarily want it to stay available, out of context, forever. The weight of our digital pasts is emerging as the central privacy challenge of our time.

But what if people could make their posts vanish automatically—making social media more of an analogue to everyday conversations that aren’t recorded for posterity? That’s the promise of services such as Snapchat, a mobile-phone app whose popularity has increased dramatically during the past year. Evan Speigel and Bobby Murphy, who met as undergrads at Stanford, came up with the idea two years ago, around the time New York congressman Anthony Weiner accidentally made racy photos of himself public on Twitter and was forced to resign. Snapchat lets users take photos or short videos and then decide how long they will be visible to the recipient. After 10 seconds or less, the images disappear forever. (Not for nothing is Snapchat’s mascot a picture of a grinning ghost.)

From the beginning, the service appealed to teenagers looking for a more private way of sending each other sexy pictures. But “sexting” alone can’t account for all 100 million photos and videos exchanged on Snapchat every day. And Mark ­Zuckerberg must worry that Snapchat addresses some misgivings people have about privacy on Facebook; in December, Facebook launched a Snapchat copycat app called Poke.

What makes temporary social media so appealing? Snapchat’s founders often remark that they wanted to give people a way to express themselves through something besides the idealized self-­portraits many feel required to maintain on social-media sites. Snapchats might be more exciting to send and receive than other social-media posts because they are ephemeral, but they are also arguably a more natural way to communicate. Whereas Facebook and Twitter record and store your every offhand observation and casual interaction, interactions in temporary social media can be something like brief, in-person conversations: you can speak your mind without worrying that what you say will be part of your digital dossier forever.

Although Snapchat’s posture as the anti-­Facebook is a large part of its allure, eventually its founders will have to confront some of the same privacy challenges that have vexed Facebook. Snapchat contains an obvious technological vulnerability: images that were meant to vanish can still be saved if the recipient uses a screen-capture feature to take a picture of the message during the seconds it appears. (If the recipient does this, Snapchat notifies the sender, but by then it’s too late to stop the image from being preserved and shared.) Moreover, while Snapchat promises to erase photos from its servers, the company’s privacy policy adds that it “cannot guarantee that 
the message data will be deleted in every case.” 
As soon as a racy Snapchat picture of a celebrity goes viral, trust in the company could be eroded.

But regardless of the fate of Snapchat in particular, the idea of temporary social media is important because the ability to be candid and spontaneous—and to be that way with only some people and not others—is the essence of friendship, individuality, and creativity. Facebook and Twitter do make it possible for their members to wall off posts from the wider world and share them only with trusted people in certain circles. But since those posts still last forever, this capacity for limited sharing is technologically insecure. To the degree that temporary social networks increase our sense of control over the conditions of our personal exposure, they represent a first step toward a more nuanced kind of digital connection—one acknowledging that our desire to share can coexist with a desire for reticence, privacy, and the possibility of a fresh start.