Aura, a government-owned tech company, has discovered what it is calling a "very big" software flaw in the Mozilla Firefox and Google Chrome web browsers.
The bug allows a user's private photos and sensitive documents such as passports, driver licenses and other identifying content to be uploaded to websites, and to be obtained by malicious hackers.
The bug was discovered by Alex Nikolova, a security analyst based in the company's Wellington office, and at the time of discovery had affected up to one in 10 browsers worldwide, or more than 300 million users.
Nikolova first found the vulnerability in February and notified Mozilla and Google (the two companies who develop the web browsers).
Both Google and Mozilla requested Nikolova not to speak publicly about the discovery until the software bug was "patched" last month.