Although Linux is a very secure platform, further hardening can be performed to make the security even stronger. The first and most important rule of security is that if you are not using a particular service, turn it off. Every unused service you disable makes your attack surface that much smaller.

To view a list of open ports on your computer and the applications that are listening to them, install the nmap package with the following shell command:

sudo apt-get install nmap

Then, execute the following shell command to list your open ports:

sudo nmap -sS -O localhost

Note that in the previous command, we're including the letter O and not a zero. After executing it, you'll see some text appear in your terminal. This text will include a list of ports and also the service that is listening on that port. By default, you may not have many ports open and listening, other than NetBIOS and a few others, and this is perfectly fine. However, if you've installed extra packages...