Zero-day

A zero-day is a flaw in software that the vendor has not discovered, which means there is no patch and no warning. The name comes from the idea that defenders have had zero days to prepare. Whoever finds one first has a window in which the usual defences simply do not apply.

Zero-days used to be rare and expensive, found by skilled researchers over weeks of work. That is what makes recent AI news notable: models are now finding and exploiting them on their own, which shortens the window on both sides. Defenders get automated tools that scan for holes, and attackers get the same thing.