In the new test, I have set to stop the WinDefend service. There are a lot of different events now (some errors and warnings) that were not in the last test, but likely due to WinDefend being stopped. Fortunately, nothing prompted it to start again by itself. So the new time frame of events (last program to install to MSIEXEC exiting) is: 15:42 - 15:52 FYI these times are just for reference only, the BIOS time is still set to its factory time. Checking through the logs, CBS is still the same, but WindowsUpdate.log is indeed different. There is nothing logged during the time period above, so stopping WinDefend did definately have an impact there. However after checking all the log files and everything else, the total time savings is about 15-20 seconds. So that isn't it. I would settle for cutting this time in half... I'll relook over the ProcMon log and see if I can come up with any other ideas. Well I did find some information regarding Windows Installer and this 10 minute period. It appears that this is NORMAL. http://blogs.msdn.com/b/heaths/archive/2006/12/08/the-windows-installer-service.aspx So now my next task is to try to stop the service, after waiting about a minute after the last program is installed. Hopefully this will also work when installing Windows Live Essentials... we shall see. Update2 Well I've got this all fixed up now. It would appear that you can't end the msiserver service if it is actively installing something. So I have altered my program to wait 1 minute, then attempt to stop the service. So far this is working out and everything is fine. I did try to research changing the msiserver service's idle timeout but came up empty on that. This will have to do for now. I also gave up trying to figure out how to check for msiserver's mutex it creates while it is installing.