If connected to the Internet, your computer could be compromised in minutes, or even less, if the firewall is disabled or otherwise turned off.

If you get a warning that it's off, take immediate action -- and I do mean immediate -- to get it working again.

To find the firewall, left-click on, in sequence, Start/Control Panel/System and Security. Left-click on "Windows Firewall," outlined here in red.

The main screen for Windows Firewall should look like this, with the green shield and white check mark for both "Home" and "Public" networks.

If you've made changes to your firewall over time and don't like the way it's working, this puts everything right again.

The Windows Firewall is a powerful security tool, and one you should use at all times.

Clicking "Use recommended settings" to the right turns on all your firewall settings automatically.

The other, to the left, says "Turn Windows Firewall on or off".

This allows you to have greater control over the firewall's behavior.

Clicking "Turn Windows Firewall on or off" in the previous screen brings you here.

The best thing Microsoft ever did for security was turn on the firewall by default way back in the days of Windows XP, Service Pack (SP) 2.