Look for port protection, self protection and easy controls in a free firewall application. A good firewall defends the computer and itself against online threats.
Computers connect to the Internet through networks, and networks use ports as entry points. It is possible for a malicious program to access your computer and personal files through an open port, so it is crucial that a firewall application is able to secure your ports. Good firewalls do so by either closing or concealing the ports to your network. A concealed port is completely invisible to outside parties and software.
A malicious program can also try to defeat your firewall completely to leave your computer defenseless. Malware may try to terminate the process that oversees the firewall or disable it from the operating system registry. A firewall application must either relaunch when terminated, or prevent malicious software from terminating it. Likewise, it must be able to fix any unwanted changes to its values in the system registry.
Because firewalls use predetermined methods to detect harmful software, they may sometimes identify harmless applications as security threats and block them. A good firewall program allows you to mark the applications that are safe and acts accordingly. Moreover, it warns you when it blocks an application.