Apple has another odd iOS bug to fix after someone found that iPhones running iOS 10 will crash upon receiving a text with just three characters, including waving white flag and rainbow emoji.

Unfortunately, there’s nothing iPhone owners can do to prevent a contact sending the malicious text, which trips up the iPhone and causes a temporary crash or, in technical terms, a denial of service.

The YouTube channel EverythingApplePro demonstrates how to copy and send the message, which in some cases can cause the sender’s device to crash also.

The bug was discovered by a computer science student with the Twitter handle @preston159, who explains the message will freeze an iPhone when that string of characters arrives via iMessage and is displayed as a banner notification.

While the recipient sees a flag emoji, a zero, and a rainbow emoji, the zero is actually a Unicode-based instruction for emoji and other characters — called a variation selector — which iOS 10 can’t process. As noted by EverythingApplePro, the emoji string doesn’t crash iOS 9, likely because it doesn’t support emoji.

“What you see in the text is the waving white flag emoji, a zero, and the rainbow emoji. The rainbow flag emoji isn’t an emoji in itself, it’s made of three characters: waving white flag, a character called variation selector 16 (VS16 for short), and the rainbow,” says Preston 159 in a writeup of the bug.

“What VS16 does in this case essentially is tells the device to combine the two surrounding characters into one emoji, yielding the rainbow flag (this is similar to how skin tone modifiers work, but not exactly the same). The text you’re copying is actually 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. Usually the phone wouldn’t try to do this, but it notices that the rainbow emoji is also there, and knows that it can combine the white flag and rainbow emoji, so it tries.”

As noted by Preston159, there are multiple ways to trigger this bug in iOS, including by sending a contact file from from an Android device. The bug affects iOS 10 through to the latest iOS 10.2.

Apple had not responded to a request for comment at the time of publication.