New York CNN Business  — 

WhatsApp has fixed a security bug that allowed hackers to take over the messaging app with a malicious GIF.

The hack could be triggered when a user opened a malicious GIF in their gallery. After the GIF was opened, the app’s contents could have been exploited, revealing previous chat history.

Devices running Android 8.1 and 9 could have been susceptible to the hack. A researcher called Awakened discovered the vulnerability and wrote about it in a blog post last week.

WhatsApp, which is owned by Facebook (FB), released a patch last month, though it said it’s unlikely anyone was actually hacked using the technique Awakened revealed.

“We have no reason to believe this affected any users, though of course we are always working to provide the latest security features to our users,” a WhatsApp spokesperson told CNN Business.

To update WhatsApp, iPhone users should open the App Store and select updates. Select “WhatsApp” and press update. On Android, users need to open the Play Story and tap on the three lines in the upper left corner. Select “My apps & games” from the menu, then select WhatsApp and tap the Update button.

The popular messaging app is often the target of hacks. In May, a vulnerability was discovered that let hackers call a person on WhatsApp and place malicious code on their phone in order to see their personal information. A patch was also released to fix this.