The black dot emoji is at the center of the latest "text bomb" string crashing the Messages app and slowing down iPhones.
All it takes is for someone to send two strings of text, and for their target to open those texts, and their device will freeze up and become unresponsive.
Awareness of the glitch is spreading thanks to a YouTube video by EverythingApplePro, which shows how to perform the attack, how a phone locks down, and how it can be rescued. I tried testing it on my iPhone 8 Plus, and the mere act of trying to load the text needed to send the attack caused Messages to seize up and stop loading images.
The strings of text affect all iPhones running the most recent version of iOS, 11.3.1, as well as those on the older 11.2 and any on the most-recent 11.4 beta releases. Since macOS, tvOS and watchOS all use the same text rendering engine, all of Apple's hardware is likely vulnerable.
What can you do? Update to the next publicly released iOS version when it's released, as Apple will hopefully patch this by then. We've reached out to Apple for comment, and will update this story if and when we get a response.
If your iPhone gets frozen by this string of text, your best bet is to force-quit the Messages app and re-open the app and delete that conversation immediately.
If you try this out for yourself, you might realize that the dot-and-hand series of characters doesn't freeze devices on its own. That's because the attack requires a second string made up of thousands of hidden invisible Unicode characters, which 9to5Mac claims "churns through CPU cycles" as your iPhone attempts to process them. That's why the older an iPhone is, the more it will slow down.
In the description field, EverythingApplePro links to the page where you can grab those strings of characters, and since we'd rather not help this code spread further, we won't link directly to that page from here.
This black dot trick started on Android devices in WhatsApp, and isn't the first text bomb to hit iPhones. This past February, Messages was similarly crashed if a device received a specific character from the Telugu Indian writing system.