...

While this may seem to be an inconvenience for you access wise, it is much less of an inconvenience than to have your system compromised and cut off due to it being an issue or worse, requiring you to rebuild the system due to it being hijacked and encrypted.

Please refer to IPTables - Basics on setting up at least IPTables Firewall that is available for most Linux based OS systems.

Keep the system updated

Just like a Windows or Mac, Linux does have security updates that need to be taken care of from time to time.

...

If this is the case, go through Security Checklist and make sure everything is secure.

If you have recently installed an network listening application, please be sure to update your firewall to restrict outside access appropriately and/or accounts related to it.

Check how exposed you are

...

You can also make use of http://nmap.online-domain-tools.com/ to test it from the internet side.

You should do this from time to time, especially after adding a new application to see what is visible.

Related articles

...