The main security issue with HTTP is the fact that all the 
traffic between the client and the server is done as clear 
text, meaning that anyone could potentially "listen" to 
your talk and grab frames and valuable information from the 
net.

To secure the transmission of information between your web 
server running IIS 6.0 on Windows Server 2003 and your 
browser clients, you can encrypt the information being 
transmitted by using SSL (Secure Sockets Layer).

Thanks 
Lokesh