I'm running Windows 8 Enterprise. A couple of times now, I've noticed multiple winlogon.exe processes running (accompanied by as many extra csrss.exe and dwm.exe). Today I saw one extra, but the first time I noticed it, there were five or six extra.
Process Explorer shows that they're all indeed C:\Windows\System32\winlogon.exe, but the extra ones have been started with the flag -SpecialSession, and that its parent process no longer exists.
Malware scans with Malwarebytes and Spybot S&D haven't shown anything, and Windows Defender has remained silent.
What is this -SpecialSession option and where could these extra instances be coming from? Google seems to know nothing about it.
Best Answer
I also see this behavior since I upgraded to Windows 8. I did an in-place upgrade over windows 7, FWIW. I don't have enough points to comment, so I'm writing this as an answer.
There is a clear pattern that each set of orphaned winlogon.exe and its child processes are likely an artifact of the new "Fast boot/hybrid sleep" feature of windows 8. By default Windows 8 does not shutdown completely. When you select "Shutdown" from the charms bar, what actually happens is that you get logged out, but instead of shutting down, Windows hibernates. This way when you turn it back on, it resumes from hibernation at your login prompt, instead of a full boot up.
Presently my oldest set of processes are 12 days old, but I shut down my computer every day. I have about 12 of these process groups.
I haven't observed any adverse side effects yet, but I'll try disabling "fast startup." I'm not convinced that it is any faster anyway.
Control Panel\All Control Panel Items\Power Options\System Settings