An iOS bug has been discovered that allows anyone to crash and freeze an iPhone or iPad simply by sending the device a series of emoji.

YouTuber EverythingApplePro uploaded a video that reveals the seemingly random string of characters – a waving white flag emoji, a zero, a rainbow, and a hidden Unicode character called “variation sector 16” (VS16), which can be copied into an iMessage conversation. When combined and sent to an Apple device, the sequence causes a handset or tablets to seize up and reboot.

Sending the string via a standard message will only affect iPhones and iPads running iOS 10.1 or below. It requires the sender to do some legwork involving iCloud and the online Notes app, but once someone receives the text, their handset will freeze without them having to open or read it.

There is, however, a second version of the exploit that works on all versions of iOS 10. It involves embedding the characters in a new contact file and sharing it via iCloud Drive with an iMessage contact, the Guardian reports. This method often isn’t as severe and usually results in the sender’s phone or Mac crashing.

French iOS developer Vincent Desmurs claims he discovered the bug, which is apparently related to Apple’s  handling of the variation selector and the emojis beside it.

“What variation selector 16 (VS16) does in this case essentially is tell the device to combine the two surrounding characters into one emoji, yielding the rainbow flag,” he said. “The text you’re copying is actually a waving white flag, VS16, zero, rainbow emoji. What I’m assuming is happening is that the phone tries to combine the waving white flag and the zero into an emoji, but this obviously can’t be done.”

Deleting the entire message string will prevent a device from repeatedly crashing, but some users have reported their iPhones constantly lock up, preventing them from taking such action. Others have reported that being sent a new message or creating one with Siri before opening Messages can fix the problem.

Apple has yet to comment on the bug, but, given that the video’s view count is closing in on one million, you can expect a patch to arrive soon.