An error was discovered on iOS that blocks the Messaging application and you can freeze or restart your phone when a specially designed website link is sent to you.
The error was discovered by software developer Abraham Masri, who gave it the catchy, albeit slightly alarmist, name of "chaiOS". It exploits the fact that messages preload any link to web pages so you can show users a preview of the page. Speaking to BuzzFeed News Masri explains that he created a website hosted on GitHub and filled in its metadata with hundreds of thousands of unnecessary characters. Masri suggests that messages are blocked when trying to load all this unexpected information, sometimes with the entire operating system.
Judging from user reports, the error does not work consistently. Sometimes it blocks messages, sometimes causes delay, sometimes freezes the device and sometimes triggers what is known as "respring" (when iOS reboots the software called SpringBoard and returns the user to the lock screen). Masri tested ChaiOS successfully on the iPhone X and iPhone 5S, and says that it only affects iOS versions of 10.0 to 11.2.5 beta 5. The error can also block messages on macOS.
Fortunately, finding working copies of a bugi chaiOS link is not easy Masri initially hosted the error on GitHub, but this link, along with other mirrors loaded by third parties, has now been removed by the site. Masri himself says he will not upload the error again, saying that he only launched it "to get Apple's attention".
No, I'm not going to upload it again. I made my point. Apple needs to take such errors more seriously.
– Abraham Masri (@cheesecakeufo) January 17, 2018
If someone has sent you a copy of the error and is currently preventing you from using Messages on your iPhone, there are a couple of solutions you can try:  Blocks the domain of the site that hosts it. So, if the link comes from GitHub, for example, go to the Safari settings, then General> Restrictions> Enable restrictions> Websites> Limit adult content> Never allow> GitHub.io.
This is not a new kind of error for the iPhone. Similar text strings or dubious web links have caused closures in iOS in both 2015 and 2016. And at this point, chaiOS is more of a nuisance than anything else.
Still, considering that the end of last year was a particularly bad time for Apple's software, we expect the company to be more alert and responsive in 2018.