When installing Ubuntu on your computer, the firewall is present but disabled. Here’s a little tutorial on how to install and configure the strongest firewall available for Linux. Most Ubuntu users do not need a firewall since by default Ubuntu does not open ports that can introduce security issues. This writer strongly suggests to install it anyway. You can never have enough protection while browsing the web. Read the following on the Ubuntu forums.
To install in terminal, type the following:
sudo apt-get install gufw
*GUFW is also available in your “software center”.
Go to your applications (or type GUFW in the search box) and open it. You can now configure the basic settings by first “enabling” the firewall.