A massive 13 GB collection of Snapchat pictures and videos has been uploaded by hackers on the notorious online forum 4chan.

The incident, now dubbed the "Snappening," has shocked users worldwide. The hack could even be bigger than the breach on the iCloud accounts of celebrities, such as Jennifer Lawrence, Kate Upton and Kaley Cuoco, among others.

Snapchat is a messaging app that allows users to send pictures and videos to each other. The major draw of the service is that the sent messages automatically delete themselves after a set period of time.

A third-party client app for Snapchat is the one being blamed for the hack, as the app has been collecting all the pictures and videos sent through it over the past few years, which users thought had already been deleted.

"We can confirm that Snapchat's servers were never breached and were not the source of these leaks. Snapchatters were victimized by their use of third-party apps to send and receive Snaps, a practice that we expressly prohibit in our Terms of Use precisely because they compromise our users' security," Snapchat said.

Users of 4chan are now developing a searchable database from the about 200,000 downloaded pictures to be able to search through the hacked images by usernames on Snapchat.

One theory for the third-party Snapchat client that was hacked is Snapsave, an app for Android that allowed Snapchat users to keep the pictures and videos.

The developer of Snapsave, Georgie Casey, denied the claim.

"Our app had nothing to do with it and we've never logged username/passwords," Casey said, adding that the app does not save Snapchat content online.

An anonymous contact informed Business Insider that the website that the hackers targeted was Snapsaved.com, which acted as a web client for Snapchat, allowing users to save online the pictures and videos that they receive.

However, what the users did not realize was that Snapsaved was adding all the content that was passing through into a giant collection, storing all the pictures and videos on a web server, including the usernames of those that sent them.

Users of 4chan who gained access to the 13 GB collection said that there was a significant amount of child pornography, as the content was sent by teenagers who thought that the files would be automatically deleted. Half of the users on Snapchat are between 13 years old and 17 years old.

The Snappening is the latest security issue for Snapchat, which has raised concerns since its launch. In 2013, researchers found out a way to obtain the phone number of Snapchat users. In February this year, hackers were able to access Snapchat to send pictures of fruit smoothies to thousands of users.