Users who had been accessing the service via a third-party app, and not the official Snapchat app, had their images intercepted.
As half of its users are aged between 13 and 17, there is concern that many of the images may be of children. However, Snapchat said its servers 'were never breached'.
The company added that they vigilantly monitor the App Store and Google Play for illegal third-party apps and have succeeded in getting many of these removed.
However, security researchers said Snapchat had to take more responsibility over user data. As or them to just turn round and say, 'It's the users' fault,' does seem harsh," said Mark James, a security specialist from ESET.