A host firewall is a software program that runs on a computer or device and monitors and controls the incoming and outgoing network traffic based on predefined rules. A host firewall can help prevent external access from unauthorized or malicious sources, such as hackers, malware, or network worms. A host firewall can also block unwanted or unnecessary traffic from reaching the computer or device, which can improve performance and security. A host firewall can be configured to allow or deny traffic based on various criteria, such as port number, protocol, application, source address, destination address, or content. A host firewall can also log or alert the user about any suspicious or blocked activity.