The defensive actions have been identified at each layer, it is necessary to discuss how these actions will be carried out for a Windows-based home Internet user. It is also important to keep in mind that the defensive posture is weakened when one does not implement the entire defense in depth strategy that is being advocated. For example,using a firewall but having either no or outdated antivirus software, leaves the system vulnerable.
Defensive Measures at Network Access Layer
This is the first layer of the defense in depth model. The defensive measures that have to be taken at this layer are:
Use a Firewall.
Disconnect from the Internet when not using it.
Use a Firewall
A firewall places a virtual barrier between the computer and hackers, who might seek to delete information from the computer, make it crash, or even steal personal information.
The firewall serves as the primary defense against a variety of computer worms that are transmitted over the network. It helps to protect the computer by hiding it from external users and preventing unauthorized connections to the computer.
For home users, a firewall typically takes one of two forms:
Personal firewall - specialized software running on an individual computer, e.g. ZoneAlarm and in-built Windows Internet Connection Firewall (ICF) etc.
Hardware firewall - a separate device designed to protect one or more computers, e.g. Linksys EtherFast Cable/DSL Router.
If user is having a home network, it is recommended that he should have both types of firewall installed i.e. hardware firewall at the router3 and personal firewall at each system using that network. But if the user is using a stand-alone PC only, then it is recommended that he should have at least a personal firewall installed on the PC.
Installing Personal Firewalls
A Personal firewall or desktop firewall is a software program that provides primary defense mechanism for the desktop computer connected to the internet.
The firewall acts like a guard, who checks everybody entering or going out of the home and based on some prior knowledge allows or disallows the people.
Once the personal firewall is being installed, it is continuously running in the background, watching out all the incoming and outgoing traffic. Simultaneously it reports to the user by giving a pop-up about the program which is trying to access the internet or conversely trying to access the user’s system. It is solely the discretion of the user that to whom or which program he wants to allow through the firewall.
Users should be exceptionally careful when allowing a particular program or file through the firewall. And have to be very considerate about which file is used by which particular program.
Why firewall is needed?
If the computer is not protected when the user connects to the Internet, hackers can gain access to personal information from the computer. They can install code on the computer that destroys files or causes malfunctions. They can also use user’s computer to cause problems on other home and business computers connected to the Internet. A firewall helps to screen out many kinds of malicious Internet traffic before it reaches to the user’s system.
Some firewalls can also help to prevent others from using user’s computer to attack other computers without user’s knowledge. Using a firewall is important no matter how the user connects to the Internet — dial-up modem, cable modem, or digital subscriber line (DSL or ADSL).
Microsoft Corporation provides Internet Connection Firewall for Windows XP SP2 users only. For the users running old versions of Windows (9x, NT or 2000), they have to select a desktop firewall according to their needs from third party.While Windows 2000 does not having a purpose-built firewall, it does have IP Security filters that can be used to make a static packet filter.
Figure-3: Protecting the Internet-connected Home PC