There two ways your computer can be attacked. Firstly by Viruses and secondly by Hackers/Crackers. To protect your computer you need Anti-virus softwareand a firewall which can be either software or hardware.

Whenever you connect to the internet, there is possibility of your computer being attacked by exploiting security holes in your computer. To find out whether your computer is well protected or you have security holes the following websites can be used to check.

Sygate Tests ( http://scan.sygate.com )

Shields up ( http://www.gre.com/x/be.dll?bhobkyd2 )

PC Flank ( http://www.pcflank.com/about.htm )

The above websites will scan your computer thoroughly and tell you whether your computer has security holes. Most of us know that Anti-virus software is required to protect one’s computer. However anti-virus software is not enough, you need a firewall to fully protect your computer.

Also installing the Anti-virus once is not enough. You need to constantly update it. Even in firewalls you have to review your policies often and update them.

What is a firewall and what are the types of Firewall?

There are both hardware firewalls as well as software firewalls. There are also firewalls with built in anti virus and spam filter softwares. Norton Internet Security, McAfee Internet Security, Zone Alarm Security Suits, Norman Internet Control are some examples of such software available today.

Your computer’s file system and protocols that are used to communicate with other computers which is called ‘Network Stack‘ are often under attack. Therefore if you prevent these two from happening your computer will be safe. To protect your file system, anti-virus software is used while to protect your network stack, firewall is used.

The files that you download from internet and the emails that you receive from others are scanned by the Anti-virus software. If virus is found in them the anti-virus software removes them. Likewise in the computer files that are opened, edited and all files in the computer are scanned and protected by the anti-virus software.

Your computer has many network ports. It is through these ports that you avail many internet services. For example HTTP protocol uses port 80 while FTP protocol uses port 21.

When you are connected to the internet, hackers can find the ports that are open in your computer and use these ports to take control of your computer. By default all ports in your computer is open. Therefore closing all the unused open ports can prevent crackers from entering your computer. This is done using the firewall.

Moreover you can ban any port that you think is unsafe. For example if you need to download files from internet buy do not want hackers to download files from your computer then you can configure your firewall to open ‘download’ service of FTP while blocking the ‘upload’ feature.

You may have heard of the MPS-Blaster worm that attacked many computers and destroyed them. This work entered these computers using port 135. This worm cannot enter those computers in which the port 135 was closed.

If you need a particular port to be open but you are scared that other hackers may use this port to enter your computer then you can use the ‘IDS – Intrusion Detection System’ feature of the firewall. IDS uses Signature based monitoring. If large amount of data is copied to the computer’s buffer through a particular port then the IDS detects this behavior and alerts the user. Note that all firewalls do not have this feature.

There are three types of firewall namely, Packet Filtering, Proxy Server and Stateful Inspection. For home users, small offices and small businesses Packet filtering firewall is sufficient. Companies with big networks can use the proxy server firewall. Stateful firewall is the latest and it is very popular and suitable in all environments.