It is a well known fact the most of the computer related fields are dominated by Microsoft. But it is not so in the case of Web Server softwares. Apache is the leader in this arena. Only about 20 percent of the servers still use Microsoft's Internet Information Server, or IIS. 

IIS and Security
IIS is famous for its terrible security record. One famous example is the case of Code Red worm that spread in the IIS servers. To solve this problem, the web masters were required to download a patch from Microsoft's website. At that time, many people switched to Apache to avoid similar problems in the future.

Most of the loopholes in security were caused due to the things that are not used on a frequent basis, and only because they were left on by default. Once infected, it could cause great damage to the system due to the fact that IIS ran with all security privileges on the system.

Hence, Microsoft decided to turn off the unnecessary services for the latest version of IIS. This made their servers much more secure. But in order to upgrade to the latest version, it was required to upgrade to the Windows Server 2003 operating system. Due to this most people are still using IIS 5.

IIS and Stability
IIS is not stable and fails under heavy loads. It does not have the ability to handle a number of connections at once. Some errors we often come across such as 'Website too Busy', these are caused due to IIS.

Use of IIS
One of the most important reason for the use of IIS is that it was created with the use of Microsoft's software. This means that the database would be made with the use of Microsoft SQL and written with ASP. Most scripts written with ASP are written in VB Script and makes it quite easy to develop dynamic websites.

ASP was the leader in creating dynamic web pages till 2001. Open source languages are quite unreliable. Most managers prefer to use the Microsoft's technology. However, companies have not yet started shifting.

IIS Alternatives
Many companies have now started to offer alternatives to IIS, that allow them to keep their ASP code. It would be a waste of time to make them redo the entire thing in PHP. The best solution to this problem has been offered by Sun. However, on the downside, this software is quite expensive. So it should be used only in cases where there is a lot of code with you in ASP language.

It is better to avoid IIS from the very beginning. It is not suitable in the long run even though it comes free with Windows.