I have had XP guests sometimes hang when doing a Windows-Update-invoked reboot. Both XP and 7 hosts, different versions of Virtualbox.
The guests get to just before the VM window would shrink to 640x480. They stop responding, no disk or network activity, just XP's peacefully-running light blue (not BSOD blue) background. If I pause/unpause or save-state/restart the VM window turns black and gets a grid of greenish yellow lines filling half the window. The VM does nothing else and I have to reset it. Then it boots up normally.
Two XP guests sometimes exhibit this behavior for now. I used to have this problem in a third guest, but it hasn't shown itself for a long while, despite still getting the same Windows updates as the two present offenders.
I have searched and found references to audio being the culprit (one guest has audio, one used to but does not now). Also, "absolute pointer" has been fingered, but I never use that setting and neither guest has ever had it turned on. I hunted thru the bug tracker but couldn't find a pertinent post, only one post actually mentioned Windows updates and the poster didn't put in logs, so the post had no activity.
So, here's the logs:
XP guest: "XPnet"; XP host, audio on, no absolute pointer, VB version 3.1.2 (this one runs all the time with no scheduled reboots, I think all the logs in the zip are from Windows-Update-induced hanged reboots)
XP guest: "Email Tester" Windows 7 host, audio used to be on but now disabled in VM settings, no absolute pointer, VB version 4.0.16 (this one is shut down by a host-induced Vboxmanage command every night; only the most recent log was a Windows-update-induced hanged reboot, the earlier logs should be normal shutdowns. I've also had this VM running on version 3.2.12 on a different Windows 7 host, with the same behavior)
The third guest that used to have this problem also was XP, audio on, no absolute pointer. It just had a Windows Update same time as the other two, but did not hang during reboot. Here's this VM's last Windows-Update-successful-reboot log for reference:
Guest Additions are current in each VM. I have not seen if other causes for in-guest-invoked reboots cause hanging, and I haven't had the hang happen when I tell the guest to reboot from the guest's Start menu or a "Shutdown -r". It seems that Windows Update is the only rebooter that causes this to happen that I've noticed so far. And I've not experienced Windows Update having a problem rebooting the physical XP PCs I have at home.
running version 3.1.2, 4.2.16, 5.0.14
Human government is like that crazy uncle who hides a quarter in his fist behind his back, then asks you to guess which fist the quarter is in...
No matter which side you choose, Left or Right, both Sides are empty.