You may not have heard of Snapchat. But if there are teenagers or 20-somethings in your life, it's a safe bet that they have.

Snapchat is a mobile app which lets users share images or videos that disappear after a few seconds. That's right -- they vanish forever in the time it takes you to read a tweet.

In a little over a year since it was released by a Stanford student and his recently graduated business partner, Snapchat has has quietly amassed millions of users and now claims to process more than 30 million messages a day. Some bloggers have called it the "next Instagram."

Not bad for a mobile tool which, rightly or wrongly, is often cited for one very specific ability -- the "sexting" of naughty images to other users. In an age when young people are constantly being warned not to post inappropriate things online, Snapchat offers a degree of freedom by letting users share unfiltered thoughts or images without much fear of reprisal.

"Like most people born before the 1990s, I'm not a Snapchat user, and I've long assumed the worst about the app -- that combining cameras; young people; and secret, self-destructing messages could only mean trouble," wrote Slate's Farhad Manjoo last week.

But increasingly, he writes, it appears possible that "teenagers are more likely using the app to safely explore the sort of silly, unguarded, and sometimes unwise ideas that have always occupied the teenage brain ... in a manner that won't haunt them forever. In other words, they're chatting with Snapchat precisely because it's not like chatting with Facebook."

Not to be outdone, Facebook last month actually launched a virtually identical social app called Facebook Poke, a mobile re-imagining of one of the site's earliest, and ultimately most ridiculed, features. But instead of siphoning users from Shapchat, Facebook's move appears instead to have launched the upstart app to new heights.

Both apps let users send images or short videos and messages via their smartphones. The sender can choose how long the message will be visible -- up to 10 seconds -- before it self-destructs.

Facebook CEO Mark Zuckerberg reportedly was part of the team that coded the Poke app, currently available only on Apple's iOS system, in only a couple of weeks. A family photo posted by sister Randi Zuckerberg purportedly showed their family playing with the app over the holidays.

But if Facebook was looking to flex its billion-user muscle to take over the instant-chat market, it doesn't appear to be working.

On Thursday, Snapchat was the sixth-most popular free app for Apple's mobile devices. Facebook Poke wasn't in the top 100. As Forbes said in a recent headline, "the kids like SnapChat because it's NOT Facebook."

A newer version of Snapchat for Google's Android devices sat at a respectable No. 33 in the Google Play store, ahead of stalwarts like Draw Something, Spotify, Fandango and Amazon Mobile. Facebook Poke isn't available for Android.

A look by analytics firm Topsy showed that mentions of Snapchat on Twitter spiraled to more than 212,000 on New Year's Day, up from about 16,000 on Dec. 20, the day before Facebook introduced Poke. Facebook Poke got 1,822 mentions on Jan. 1, according to Topsy.

So, does that mean young, socially savvy users are sending millions of racy pictures of themselves through cyberspace every day?

It's difficult to say. Technological advances and nudie shots have shared a strong, if secretive, relationship for centuries. From the printing press to pay-per-view to VCRs, new tech (particularly the kind that creates new levels of privacy) has always been followed closely by folks figuring out how to personally or professionally use it to get dirty.

Read: In the tech world, porn quietly leads the way

There are clear, and sometimes ugly, signs that sexting is common on Snapchat.

"Snapchat Sluts," a Tumblr blog full of nude and semi-nude images, was started up last month by a "party photographer" who says he put out an open call for salacious shots on Twitter and was overwhelmed by the response. Another Snapchat-themed blog on Tumblr is filled with complaints about male users sharing photos of their genitalia.

Snapchat users may think their naughty images will never come back to haunt them. But people can still grab screenshots from their phones, even though both Snapchat and Facebook Poke notify the sender if the recipient of an image takes a shot of it.

And last week, Buzzfeed exposed an apparent security flaw that it says lets recipients retrieve videos sent via Snapchat.