Sorry for my reply!
Since your ask is about "Computer protection" wording, but topic is placed under "home security" community board (F-Secure SAFE) - does your concern about Business solution or about Home solution?
If it is a Business solution, then there is a community board where, maybe, such subject is discussed:
But if your ask is about "Home solution", then what is your requirement for platform? Windows?
It is not possible to block all internet sites. The reason being that PSB is a Cloud based solution, and also utilizing web browser interface, therefore requires persistent internet connection through port 80 (http) and port 443 (https). PSB web content also links to Cloud ORSP database, for URL reputation scanning.
PSB can restrict web browsing based off the category filtering setting (example: "drugs", "adult", "games" etc.). If the website fits into those categories, browsing can be blocked. Be sure the following settings are also applied for restrictions to be properly enforced;
Another workaround is to deploy a http proxy in your environment as a second layer filtering.
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