What does an "open port" mean?

Think of an apartment building

Your home internet connection is like a building with about 65,000 numbered doors. Each door is for one kind of service. A "port" is just one of those numbered doors.

What "open" means

A door is open when something behind it answers a knock. Most doors are shut and stay shut. Our check knocks on a short list of doors that criminals like to try, and tells you which ones answer. We only knock. We never try to go in.

Why an open door is not always bad

Some doors are open for good reasons, like a web page you set up on purpose. The problem is a door that is open and you did not know about it, because strangers can try it too.

The doors we check

How it gets closed

Most of the time the door is opened by your router (often because a gadget asked it to, using something called UPnP) or by a setting on one computer. Closing it means turning that setting off. Our fix guides show you how, or you can ask your internet company to do it.