Snapchat updated its photo sharing app for Android and iOS to better protect the privacy of users, a week after hackers exposed a vulnerability.

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

The 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.

The change to the Find Friends functionality allows users to opt-out of linking their phone number with their user name. The update requires Snapchat users to verify their phone number before using the Find Friends services.

In the blog post announcing the change, the company apologised for any problems the issue may have caused and said it will continue to make improvements “to prevent future attempts to abuse our API”.

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.

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 would therefore have been unwelcome.

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.