What just happened? Twitter has banned all animated PNGs (APNGs) from its platform to stop trolls using the images to trigger seizures in photosensitive people. The site has discovered a bug that lets users bypass its autoplay protections, allowing multiple animated images in a single tweet using the file format.

“We want everyone to have a safe experience on Twitter,” the company said in a tweet. “APNGs were fun, but they don’t respect autoplay settings, so we’re removing the ability to add them to Tweets. This is for the safety of people with sensitivity to motion and flashing imagery, including those with epilepsy.”

During November, which was National Epilepsy Awareness Month, the Epilepsy Foundation revealed that some Twitter users mentioned the organization and its hashtags in tweets that featured flashing or strobing images. It’s not clear how many people, if any, were affected by the attacks. While APNG files were not used in this case, Twitter has moved to make sure they aren’t utilized this way in the future.

Back in 2017, a man was charged with aggravated assault with a deadly weapon after sending a journalist who has epilepsy a tweet containing a strobing GIF. Kurt Eichenwald had an eight-minute epileptic seizure after viewing the message and suffered from after-effects for several months.

With most people using GIFs in their tweets, the change is unlikely to be noticed by the majority of users, and existing APNG files already uploaded to the site won’t be removed. Twitter says it is looking into “building a similar feature that’s better for you and your Twitter experience.”