Security history reports info that someone signed in after I shut down desktop computer?

I logged off before 7 last night and shut down my desktop computer.

 

I have a wired connection with ethernet cable. No wireless devices ...no one else lives with me. doors locked.

 

Security history shows someone logged in approximately two hours after I shut my computer down and was on my computer

 

norton 360 reporting (info) a few updates and then this mystery user logged off at around midnight.

 

so.........someone was monkeying around on my computer from 8:30 until midnight while I was asleep with no one else in the apartment.

 

anyone care to explain why this intrusion wasn't stopped by either my norton 360 (boot set to aggressive) quick scans run everyday...or my mbam updated and quick scans run everyday...or my superantispyware updated and quickscans run everyday?

 

I have a cisco dpc3008 cable modem.    wired directly to my desktop computer via ethernet cable.

 

????

 

thanks!

 

just me again

 

emachines el1850G 3.60 mghrz

2 gb ram

windows 7 sp1 home premium desktop 64 bit os

wired connection via ethernet cable

norton 360 21.1.0.18

mbam free

superantispyware free