JSI Tip 3625. Why do some versions of Internet Explorer have a two letter version suffix?

When you press Help / About Internet Explorer, some site installations of Internet Explorer have a a two letter suffix following the version string?

The version number has the following format:

major version.minor version.build number.sub-build number XX

XX is normally blank, but can contain a two letter string, if the installation of Internet Explorer 5.x was customized using the IEAK (Microsoft Internet Explorer Administration Kit):

IC = Internet Content ProviderIS = Internet Service ProviderCO = Corporate Administrator

Internet Explorer 4 or later also displays an Update Versions line that lists all the installed updates/hotfixes. Here is a list of Internet Explorer version numbers, starting with the release of IE 4.0:

   Version          Product   -----------------------------------------------------------------   4.71.1712.6      Internet Explorer 4.0   4.72.2106.8      Internet Explorer 4.01   4.72.3110.8      Internet Explorer 4.01 Service Pack 1 (SP1)   4.72.3612.1713   Internet Explorer 4.01 Service Pack 2 (SP2)   5.00.0518.10     Internet Explorer 5 Developer Preview (Beta 1)   5.00.0910.1309   Internet Explorer 5 Beta (Beta 2)   5.00.2014.0216   Internet Explorer 5   5.00.2314.1003   Internet Explorer 5 (Office 2000)   5.00.2614.3500   Internet Explorer 5 (Windows 98 Second Edition)   5.00.2516.1900   Internet Explorer 5.01 (Windows 2000 Beta 3, build 5.00.2031)    5.00.2919.800    Internet Explorer 5.01 (Windows 2000 RC1, build 5.00.2072)   5.00.2919.3800   Internet Explorer 5.01 (Windows 2000 RC2, build 5.00.2128)   5.00.2919.6307   Internet Explorer 5.01 (Also included with  Office 2000 SR-1, but not installed by default)   5.00.2920.0000   Internet Explorer 5.01 (Windows 2000, build 5.00.2195)   5.00.3103.1000   Internet Explorer 5.01 SP1 (Windows 2000)   5.00.3105.0106   Internet Explorer 5.01 SP1 (Windows 95/98 and Windows NT 4.0)   5.00.3314.2101   Internet Explorer 5.01 SP2 (Windows 95/98/ME and  Windows NT 4.0)   5.00.3315.1000   Internet Explorer 5.01 SP2 (Windows 2000)   5.50.3825.1300   Internet Explorer 5.5 Developer Preview (Beta)   5.50.4030.2400   Internet Explorer 5.5 & Internet Tools Beta   5.50.4134.0100   Windows Me (4.90.3000)   5.50.4134.0600   Internet Explorer 5.5   5.50.4308.2900   Internet Explorer 5.5 Advanced Security Privacy Beta   5.50.4522.1800   Internet Explorer 5.5 Service Pack 1   6.00.2462.0000   Internet Explorer 6 Public Preview (Beta)

See tip 2508.