The usernames and phone numbers for 4.6 million Snapchat accounts have been downloaded by hackers, who temporarily posted the data online.
A website called SnapchatDB released the data but censored the last two digits of the phone numbers.
It has since been taken offline but a cached version is still available.
The hack comes days after an Australian firm, Gibson Security, warned of vulnerabilities in Snapchat’s app which it said could be exploited by hackers.
Gibson Security said it was not involved in the hack: “We know nothing about SnapchatDB, but it was a matter of time till something like that happened,” the firm tweeted.
The hackers behind the website that published the data said they had exploited the security flaw highlighted by Gibson Security.
“We used a modified version of gibsonsec’s exploit/method,” they were quoted as saying by tech blog, Tech Crunch.
Snapchat has grown in popularity as an app that allows people to share pictures, safe in the knowledge they delete themselves after being viewed.
It has a feature called Find Friends, which allows users to upload their address book contacts to help find friends who are also using the service.
In its report published on 25 December, Gibson Security warned that a vulnerability on the Snapchat app could be used to reveal the phone numbers of users.
The firm said it had first warned Snapchat about this four months ago, adding that “nothing had been really been improved upon”.
Read more: BBC