This is pretty well known and lots of others have posted about it over the years, but for the sake of completeness for those who read the last post and don’t know this already…
Often when you try to attach to the w3wp.exe process and debug an assembly there are multiple instances from which to choose. How do you know which one to pick?
Open a command prompt and run the iisapp.vbs script with no parameters as follows:
It will output a list of the currently running application pools and the associated PIDs.
Author: Doug Ware