The filter computer is probably a Firewall. I have several. Every computer in my home has some form of Linux installed. All business is done on ethernet-wired computers with firewalls between them and the wireless network. The Linux boxes have internal firewalls that let things out but do not let anything in. I have one device that has Windows 10 installed. It is used for only two purposes. Updating GPS and running an R/C Flight simulator. Linux is installed on a second drive in this system, and it is encrypted, so nothing in Windows can access it. I don't run any Microsoft software anywhere.
I only used Windows in a lab environment when I was working, never on my desktop. OS/2, Linux, and Solaris were what I used. I drove the desktop support people crazy. I could see them, but they could not see me.
Passwords are incredibly important. I worked in desktop support for a couple of years. I could usually guess or locate people's passwords. Not only were most of them simple, but many times, they were written down on a postit note and stuck somewhere. On the bottom of their keyboard was a popular spot. I have found the list of passwords stuck on a monitor.
For many years, I ran a Linux box outside the company firewall. I could sit and watch them try to break in. All day every day 24/7. There were so many attacks I had to turn the alerts off. I was getting hundreds and, on some days, thousands of emails.