Contact information belonging to 4.6 million users of photo sharing app Snapchat was published by hackers, despite the app maker’s claim to have fixed the vulnerability in question.

An anonymous group posted phone numbers and user names on a website called SnapchatDB, which was quickly closed down. It redacted the last two digits of phone numbers, stating the material was published to “raise awareness” around the issue.

The hackers said the information was acquired through “a recently patched Snapchat exploit”, which was dealt with too late. It added that companies trusted with user information “should be more careful when dealing with it”.

The vulnerability was made public by Australian security research group called Gibson Security on 25 December. It claimed to have informed Snapchat of the issue several months ago but that the app maker did not respond.

Snapchat responded to Gibson’s findings by saying it has taken steps over the past year to make it more difficult for people to create a database of phone numbers which could theoretically be matched to user names.

“We recently added additional counter-measures and continue to make improvements to combat spam and abuse,” the company said in a blog post.

Gibson said on Twitter it had no involvement with the release of the user information on SnapchatDB.

Snapchat, which deletes images seconds after they have been viewed and is particularly popular with young users, is currently subject to speculation about a possible acquisition. Concerns about privacy are therefore unlikely to be welcome.

Although it doesn’t yet generate revenue, the company reportedly rejected a $3 billion bid from Facebook in November. Evan Spiegel, Snapchat’s co-founder and CEO, is believed to be waiting for user numbers and messages sent via the service to increase further, in order to push for a higher valuation.

In June, Snapchat raised $60 million, in a transaction which valued the company at $800 million. By September, the company said usage had almost doubled to 350 million messages per day.

Facebook is believed to be interested in Snapchat due to its messaging capability and young user base. The social network’s business is increasingly generating revenue from mobile advertising but it recently stated that fewer teenagers are using its service.