The next big cyberthreat isn't ransomware. It's killware. And it's just as bad as it sounds.

Even as most Americans are still learning about the hacking-for-cash crime of ransomware, the nation’s top homeland security official is worried about an even more dire digital danger: killware, or cyberattacks that can literally end lives.

The Colonial Pipeline ransomware attack in April galvanized the public’s attention because of its consumer-related complications, including long lines at gas stations, Homeland Security Secretary Alejandro Mayorkas said in an interview with USA TODAY's Editorial Board last week.

But, "there was a cyber incident that very fortunately did not succeed," he added. "And that is an attempted hack of a...