echondo: Build a Windows Server/IIS/ASP.NET web server, with the antivirus of your choice and place it directly on the internet, not behind any kind of Linux proxy server, and you'll quickly see how insecure Windows really is.
Then, note that Linux has ~90% marketshare of webservers(and equally high marketshare in proxies, DMZs, etc...), with multiple different web servers like Apache, Nginx, Tornado, etc... multiple different web scripting languages like PHP, Perl, Python, and virtually none of these servers have any kind of antivirus installed. Despite the massive diversity and choice in application stacks be developed by multiple different teams all over the world, they all (except for crappy Java, but I digress)manage to be perfectly secure.
That, my friend, should tell you how insecure Windows really is, you shouldn't need an antivirus in a secure operating system. If hackers could be readily pwning those ~90% of web servers, they would, the market share argument Windoze fanboys make about Linux on the desktop is totally invalidated by Linux's market dominance of internet-facing servers.