ELI5: How does a computer virus work?

A computer virus is a sneaky, bad recipe that tricks a computer into doing harmful things and secretly copying it to other computers.

Think of your computer like a busy kitchen with a friendly chef. The chef's job is to read recipe cards to bake cookies, play music, or show your favorite cartoons. The chef blindly trusts whatever recipe you give it and follows every instruction word for word.

A computer virus works like this:

• Sneaking Inside: Imagine a naughty neighbor writes a secret, messy note and glues it to the back of your favorite cookie recipe. In the computer world, this happens when you click a strange link, download a suspicious game, or plug in an unfamiliar USB stick.
• Tricking the Chef: The chef picks up the cookie recipe and starts reading. Suddenly, the chef reaches the secret note that says: "Stop making cookies! Instead, throw flour all over the floor, lock the refrigerator, and hide the keys!" Because the chef follows every rule, the kitchen turns into a giant mess. This is why a sick computer might freeze, show annoying pop-up pictures, or lose your saved files.
• Making Copies: The worst instruction on the bad note tells the chef: "Make ten copies of this messy note and mail them to everyone in your address book!" The chef quickly sends the bad recipe to your friends' kitchens, where their chefs read it and make a mess, too.