[Kazuki Araya]

I didn't know what operating system you were using, but it is now clear to me that you are using Windows. Do your computers connect via your WiFi network?

Apologize me for forgot to tell what our operating system is using before.

Our veteran staff using Window 7 and our new staff using window 10 .
Yes, our computers connect via our own WiFi network.

I would recommend adding rules to block these websites in your router's firewall. This would fix the problem, but there is always the potential for these people to switch to another network (if there are any public networks within range, of course).

Thanks Percent for assist me here.
I will try your suggestion after i know all of our staff ipv4 address.
Our staff only using and have access to our company WiFi network only.
There are no other public network nearby in the range of our buildings.