Most computer viruses are annoying. Some steal passwords. Some encrypt files and demand money. In 2010, security researchers found one that did something different: it broke physical machines.

The worm became known as Stuxnet . It is still the clearest example of malware crossing the line from digital damage to real-world destruction.

The target was not a website

Stuxnet was aimed at Iran's uranium enrichment facility in Natanz . The centrifuges there spun at very high speeds to enrich uranium. Stuxnet's goal was to interfere with those machines quietly.

That made it different from ordinary malware. The attackers did not just want data. They wanted to slow a physical industrial process without making the operators understand what was happening.

It entered through the real world

The Natanz systems were not supposed to be easy to reach from the internet.…