At the end of 2013, the usernames and phone numbers of 4.6 million Snapchat users were leaked exposing the security vulnerability of the app. Snapchat allows users to upload their address book so that their contact numbers could be matched with their respective usernames in Snapchat’s database.
If you were to input a lot of random phone numbers in your Snapchat contact list, you would easily get the matching usernames. Exploiting this loophole, 4.6 million username and phone numbers were “hacked” and leaked online. Amidst widespread criticism, this incident will probably serve as a push to Snapchat team to patch up their security hole asap giving us a new and improved Snapchat experience.
If you think your Snapchat account has been hacked you can check it here.
Most of the leaked numbers are of American users and people outside should not worry much about it. If you’ve found that your account has been compromised you can delete it in this link: Delete Snapchat Account
UPDATE: With the latest Snapchat update you have the option to unlink your phone number to your username. Another added security measure requires users to verify their phone numbers while using the Find Friends feature.