A shocking new cyberattack has been called the worst in U.S. history, and it involves Chinese hackers. This month, U.S. authorities accused a hacking group named Salt Typhoon, which is believed to be linked to China, of breaking into American telecom companies and stealing sensitive data. This hack lasted for months, and it targeted communications that were being used for U.S. law enforcement purposes.

The hackers didn’t just steal regular information—they managed to intercept text messa...