Summary:

• **What is a Zero-Day?** Apple found and fixed a very old security problem in iOS (the software that runs iPhones) that hackers may have been secretly using to spy on people. A "zero-day" is a bug that nobody knew about until it's discovered, which makes it extra dangerous because there was no way to protect against it before.

• **Why This Matters** This bug has been hiding in iPhones for about 10 years, and bad people might have used special spyware software to sneak into people's phones and watch what they do. Apple released an update to fix this problem, so it's important for people to update their iPhones to stay safe from hackers.