A firewall is a system installed to ensure the network security. It could either be a hardware or a software base. The firewall is program to control both incoming and outgoing traffic of the network based on rules set. It acts as a barrier from the outside untrusted networks.
A firewall would be the answer because as you go to a website, the firewall scans the website and if it detects anything suspicious then usually it will block you from that site or warn you about it and ask if you want to continue or not.
