How good does Windows Firewall work to protect your computer from getting viruses when surfing the web?
For most home internet users, your router acts as a pretty good firewall so generally Windows doesn’t have much work to do. But if you plug straight into a modem or use public hotspots, Windows firewall generally does quite a good job at stopping stuff connecting when it shouldn’t. I’m not aware of any advantages gained by using a third party firewall vs the one that’s built into windows!
It depends on the nature of viruses. Some are easily blocked and some like various Trojans can be easily passed through sneakily by being attached to various other emails or files that a user downloads off the internet.
But the majority of the viruses are taken care of by the firewall of windows defender.