Others here will be able to tell you better than me, but I do not believe that a restart can log you back in to Windows if you have a login password set, not even after any Windows Updates.
What I am not sure about is whether both Windows Defender and AVG have been loaded by the time the Windows logon screen appears. What I mean is, if the Windows environment continues to load up when the logon screen displays, (I think it does), does that allow utilities like Windows Defender and AVG to perform scans in the background.
When I turn my PC on and I eventually see the logon screen I have noticed that, if I logon immediately, my Desktop appears almost instantly. However, if I delay a few seconds my Desktop takes longer to load, as if Windows has become bored with waiting for me and has continued on to other tasks. The Desktop then has to wait for a chance, (an interrupt or something like that), before it will display.
Some utilities do load up. My ZoneAlarm firewall loads its TrueVector service almost immediately after POST to protect the system from hackers as the broadband connection connects before Windows loads.
However, your test surely was, when you returned to the laptop and opened the lid, was Windows fully loaded and functioning, or was it at the logon screen? If that colleague really does not have a password, and if there are no other accounts on the system that do not have a password, but Windows was fully loaded, then it seems my belief is false.
Nothing to do with me of course, but I would never leave my own computer on and unattended for such a long time. It seems your laptop was in an office environment? I wouldn't do that.
I have a Toshiba laptop with Windows XP Professional. One night, I left my laptop on so I could download a few things (I just close my lid and the broadband connection remains on ? when the lid is opened, there is no requirement to enter a password to log on or anything like that).
I was out of the office for a few days. But during that time, someone tried to access my laptop to print a document by inserting a pen drive into the USB port. He later claimed to a colleague that he could not access the laptop because it prompted him for a password, which is not possible normally since I did not password protect the computer when opening the lid. However, I went through the Event Viewer and noticed that Windows had downloaded and installed a security update the same night I left it on. Apparently, this required a system restart.
I thought I was lucky, because normally if the system is restarted, it will ask for a password to log on. However, when I looked at the Event Viewer in closer detail, I noticed that Windows Defender still conducted the daily scans even after the restart and when I looked at my AVG Antivirus log, it showed that the daily scheduled scans occurred even after the apparent system restart.
My questions are as follows:
1. When Windows initiates a restart, would it go to the screen where it asks me for my password or for a restart due to installation of a security update, does it take you directly to the desktop without asking for a log in password?
2. If it does ask for the password before logging in, then how can Windows Defender and AVG still run if not logged in? When I got back, I tried restarting my laptop moments before the scheduled daily AVG scan and just left the screen at the place where it prompts for the log in password (I did not enter it though). Then, after 20 minutes, I entered my password to log in to see if AVG had initiated and it turns out that it had not. Which leads me to believe that after the system was restarted due to the Windows security update, it automatically logged my back in without a password, and that is the only way AVG and Windows Defender could have run after that. If that is the case, I am worried about someone accessing my files and/or placing malicious software. I had run AVG antispyware and Panda Activescan after the incident, but it did not find anything. However, a few days later, I downloaded Spyware Doctor and it found Trojan-PWS.OnlineGames.KW which made me even more nervous.
Do I have anything to worry about?