For a couple of years now, the artificial intelligence community has been warning that there is a chance their work will go south and humanity will end in a conflagration worthy of a superhero movie.

Friday brought a pointed reminder that disaster is at least as likely to creep in quietly, perhaps from a piece of technology so mundane that hardly anyone knows it exists.

Our lives are built on systems piled on systems. As we board airplanes, cross bridges, pay bills, download updates, track our children at camp and generally try to make it through the day, we take them for granted.

Until they fail.

This week’s global software outage, immediately proclaimed as the biggest in history, was not caused by terrorists or A.I. or rogue hackers demanding billions in ransom. It wasn’t even done as a lark by some off-the-charts smart teenager. Those are the Hollywood versions. Instead, it was a routine upgrade that somehow went off the rails.

CrowdStrike, a Texas company, specializes in protecting corporate clients from cyberthreats. It has been very successful at this. This time, though, the threat came from CrowdStrike itself, a problem for which it seemed unprepared.

The trouble began with a small Windows software update CrowdStrike sent to its customers on Thursday night. For some reason, this crashed every computer it touched. “Your PC ran into a problem,” users were cheerily informed. “It looks like Windows didn’t load correctly,” messages announced. The backdrop was the color of a perfect sky, also known as the Blue Screen of Death.