The 'hack' was created by vincedes3, an iOS and Windows developer and security researcher. It involves the sending of a contact card (VCF) that contains a very complicated and large amount of text. When the recipient tries to open the file, it causes the app to freeze. Killing the app or rebooting will not fix the issue as Messages tried to reload the VCF every time it opens.
To make matters worse, the sender can't provide instructions on how to fix it because the recipient's Messages app no longer works.
If you've received a contact card named 'vincedes3.vcf', do not open it.
If its too late and your Messages app is already broken, there are a few methods that may work to fix it. The easiest seems to be asking Siri to send a text message. Before you send it, tap the text bubble and Messages will open, allowing you to delete the malicious contact card.
Take a look at a demonstration of the attack below.