This reasoning backfires when one considers that Apache is by far the most popular web server software on the Internet. According to the September 2004 Netcraft web site survey, [1] 68% of web sites run the Apache web server. Only 21% of web sites run Microsoft IIS. If security problems boil down to the simple fact that malicious hackers target the largest installed base, it follows that we should see more worms, viruses, and other malware targeting Apache and the underlying operating systems for Apache than for Windows and IIS. Furthermore, we should see more successful attacks against Apache than against IIS, since the implication of the myth is that the problem is one of numbers, not vulnerabilities.
Yet this is precisely the opposite of what we find, historically. IIS has long been the primary target for worms and other attacks, and these attacks have been largely successful. The Code Red worm that exploited a buffer overrun in an IIS service to gain control of the web servers infected some 300,000 servers, and the number of infections only stopped because the worm was deliberately written to stop spreading. Code Red.A had an even faster rate of infection, although it too self-terminated after three weeks. Another worm, IISWorm, had a limited impact only because the worm was badly written, not because IIS successfully protected itself.