New definition of Anonymous Users performance counters in IIS 6.0 versus IIS 5.0(Kristofer Gafvert, July 31, 2007)
If you migrate from Windows 2000 and IIS 5.0 to Windows Server 2003 and IIS 6.0 you will notice that the "Current Anonymous Users" performance counter will show a much smaller value indicating fewer anonymous users. Can it really be true that you get fewer visitors to the website when you are moving to IIS 6.0?
The definition of "Current Anonymous Users" is changed
Of course not, a server change does not decrease the number of visitors (unless the migration caused a long down-time, which will obviously affect the number of visitors keen to come back to your website). The reason for this lower number of anonymous users in IIS 6.0 has to do with the definition of "Current Anonymous Users".
In IIS 5.0, "Current Anonymous Users" is the number of current anonymous HTTP connections. Only once the connection was closed (due to time out or is explicitly closed), the number decreased. In IIS 6.0, "Current Anonymous Users" is the number of requests currently being processed. Once the request has been processed, the number of "Current Anonymous Users" decreases. So in other words, IIS 5.0 counts each connection as a user, whereas IIS 6.0 counts each request as a user. Since the processing time is a lot shorter than the time the connection is open, the number of "Current Anonymous Users" will be smaller in IIS 6.0 compared to IIS 5.0.