How To Do it..

The Wikipedia definition of Open Source is: 

"Open source is a development methodology, which offers practical accessibility to a product's source (goods and knowledge). Some consider open source as one of various possible design approaches, while others consider it a critical strategic element of their operations. Before open source became widely adopted, developers and producers used a variety of phrases to describe the concept; the term open source gained popularity with the rise of the Internet, which provided access to diverse production models, communication paths, and interactive communities.

This is not a hard thing to do. There are a lot of full featured antivirus out there that work really good and will not cost you a penny.

First of all you need to know the diffrence between an Antivirus software and an Antispyware software they are two different things and sometimes they come bundeled together but other times you will need to install 2 difrerent programs.

Here is a list of some of the most used Free Antivirus you can find and download from the net.