Firewalls basically work as a filter between your application and network connection. They
act as gatekeepers and as per your settings, show a port as open or closed for communication.
You can grant rights for different applications to gain access to the internet and also in a reverse
manner by blocking outside applications trying to use ports and protocols and preventing attacks.
Hence you can block ports that you don't use or even block common ports used by Trojans.
Using Firewalls you can also block protocols, so restricting access to NetBIOS will prevent
computers on the network from accessing your data. Firewalls often use a combination of ports,
protocols, and application level security to give you the desired security.
Firewalls are configured to discard packets with particular attributes such as:
Specific source or destination IP addresses.
Specific protocol types.
TCP flags set/clear in the packet header.
Choose the firewalls which have the ability to ward off all intrusion attempts, control
applications that can access the internet, preventing the malicious scripts or controls from
stealing information or uploading files and prevent Trojans and other backdoor agents from
running as servers.
The purpose of having a firewall cannot be diminished in order to gain speed. However,
secure, high-performance firewalls are required to remove the bottleneck when using high speed
Internet connections. The World-Wide-Web makes possible the generation of enormous amounts
of traffic at the click of a mouse.
Most of these firewalls are free for personal use or offer a free trial period. All the personal
firewalls available can't ensure 100% security for your machine. Regular maintenance of the
machine is needed for ensuring safety.