Snapchat is in the headlines again for allegedly leaking out nude photos of users. They strictly deny that there was any breach of their servers, and blame third party applications for leaking this data. This might be the case, but it is not enough to take them off the hook, especially given that their product is mostly about confidence. There are more and better instant-messaging apps out there, and whoever uses Snapchat uses it exactly so such events do not happen, whatever the excuse is.
I have no idea what exactly happened, if at all, but if a third party app got to access Snapchat data, then this Snapchat data was either
obtained by the third-party app on the user device, or
obtained by the third party app by impersonating the legitimate Snapchat app against the Snapchat server.
On a typical (i.e., un-rooted) Android or iOS device, apps can store their data so it is not readily available to other, unauthorized, apps; it would have been careless to leave such photos behind for the asking. On the other hand, Snapchat were accused several months ago for improperly authenticating their clients by the server, allowing easy impersonation of Snapchat client apps. I was quoted in USA Today yesterday addressing the need to properly authenticate clients.
Lastly I will add that there is also the possibility that no breach has ever occurred, and that the entire image dump is a hoax. Time will tell.