A single text message could cause your iPhone to temporarily freeze and restart, according to several reports. The troublesome text won’t affect devices running Apple’s latest software, iOS 10.2, but could lock up phones running earlier versions of iOS 10.

The string of text that is said to be triggering this effect includes a waving white flag emoji, a zero, and a rainbow emoji, as YouTube channel EverythingApplePro demonstrates, which says it heard about the bug through a tip. French iOS developer Vincent Desmurs claims to have discovered the hack, according to The Guardian. Although the message may only show those three characters, the text capable of causing iPhones to freeze also includes an invisible character called a variation selector, which The Guardian says can be copied into any iMessage.

Upon receiving the message, the touchscreen and buttons on the recipient’s iPhone become unusable for a short period of time, after which the device may reboot. This can last for about a minute, according to The Telegraph, while the YouTube video notes it could take about three to five minutes. The string of characters is said to cause a lockup even if the victim doesn’t open the message in question.

Apple hasn’t responded to a request for comment, and TIME was unable to reproduce the issue on an iPhone 7 running iOS 10.01. But there is an explanation for what appears to be causing the crash. Since a rainbow flag emoji doesn’t officially exist, a targeted iPhone tries to combine the code for both the white flag and the rainbow symbols using the variation selector, the reports note. It’s unable to do so in this scenario because of the zero in the middle, which is said to be causing the freeze.

Those who have updated to the latest version of Apple’s iOS mobile operating system aren’t vulnerable to this specific problem. Still, EverythingApplePro says it created a shareable file that reportedly produces a similar effect on devices running the new software.

This isn’t the first time iPhone users have reported that their devices have become frozen after receiving a specific text message. A similar bug was reported last year, which made it possible to crash an iPhone by sending message that included a certain string of characters in English, Arabic, Marathi, and Chinese. In November, a video surfaced that would cause Apple smartphones to slow down and eventually stop working for a few minutes when played in Safari.

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