Towards the end of 2013, around 4.6 million Snapchat usernames and phone numbers were exposed after the app got hacked. Snapchat said that they issued a patch for the hack, but they did not apologize for the issue until today (bad PR move).
Snapchat issued an updated for iOS and Android that improved upon the Find Friends functionality. It allowed Snapchat users to opt out of linking their phone number to user names. The option is available under Settings > Mobile #.
Here is what Snapchat wrote:
“Our team continues to make improvements to the Snapchat service to prevent future attempts to abuse our API. We are sorry for any problems this issue may have caused you and we really appreciate your patience and support. Snapchat issued an updated for iOS and Android that improved upon the Find Friends functionality.”