@Chikipi, that’s cute. Way wrong… but cute. You might be interested to read about denial of service attacks.
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IP addresses are like street addresses. Simply “knowing” one doesn’t tell anyone much of anything. Plus the fact that your computer often times goes through a set of routers that each acts as a door. Your router’s IP address might be visible, but not necessarily anything behind it.
With your IP address alone, some random person could probably determine your internet service provider and the city you’re in.
If someone attempted to connect to your computer at that IP address, they could then check for available services hosted on your machine (like telnet, http, ftp, ssh, torrent, bonjour, etc.). If your machine hasn’t been kept up to date with security patches, a malicious person could attempt to hack their way in through a vulnerability in one of those services.
Having a firewall in place helps prevent malicious attacks or even just innocent pinging of ports.
My point is, just like your house has a street address that someone can find out, it doesn’t mean that they can actually get into your house. You have doors and windows you keep shut, you’ve got locks, you’ve got a dog, an alarm system, and a neighborhood watch. On your computer, you’ve got many analogues to each of those things, too.