Twitter pulled down two brightly flashing Vine videos on Friday after it was criticized by epilepsy campaigners for uploading “massively dangerous” ads. The videos, which reportedly consisted of looping, rapid succession of bright colors, were designed to advertise Twitter’s #DiscoverMusic campaign.

“Twitter's ads were dangerous to people living with photo-sensitive epilepsy,” Simon Wigglesworth, deputy chief executive of U.K.-based charity Epilepsy Action, told BBC. Earlier, on Twitter, the organization had urged the social media corporation to take down the ads, following which a Twitter representative responded saying that the company had removed them.

However, the ads reportedly remained online for 18 hours before being pulled down.

“Eighty-seven people are diagnosed with epilepsy every day and that first seizure can often come out of nowhere,” Wigglesworth reportedly said. “For a huge corporation like Twitter to take that risk was irresponsible.”

According to the World Health Organization (WHO), approximately 50 million people worldwide have epilepsy. Epileptic seizures can be triggered by flashing lights and bright colors, making the auto-playing Vine ads particularly dangerous for patients.  

The U.K.’s Advertising Standards Authority told BBC that its rules prohibited uploading ads that “might cause harm to people with photosensitive epilepsy.”

Earlier, in 2007, Epilepsy Action had raised concerns over a segment of animated footage promoting the 2012 Olympics, which allegedly displayed a moving multi-colored pattern that stayed on television screens for nearly six seconds. The footage was later removed after the Olympics organizing committee received complaints that it was triggering seizures.