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I was just browsing around when at once I got messages that UAC, windows defender, Avast, etc. got turned off, without me doing anything. Then my PC turned by itself. I'm now running virus scans and I checked my eventlogs, but found nothing yet.

Windows Update also failed to install a new definition after I rebooted.

Any idea what this could've been?

EDIT: Forgot to mention that everything was turned on again after rebooting. I have since the reboot got nothing abnormal.

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I would run a bunch of different scans...sounds viral to turn that stuff off. – KCotreau Jun 30 '11 at 12:02
up vote 3 down vote accepted

Sure sounds like malware. I would add using a bootable malware tool or connecting the hard drive to a different computer with known good AV software. If this is a rootkit of some kind, you will probably never find it using an AV product running on the infected drive.

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This. Either there was cascading software terminations (highly unlikely), or you got a virus which is now hiding itself nicely. Scan the HDD from another computer. – cp2141 Jun 30 '11 at 13:57

Did you check the system error logs? Generally they can point to some evidence of what started the cascading failure. If it was just a software failure, it could've been an AV driver that failed and then for safety, the AV restarted the system automatically. I'm not aware of a specific AV that does this, but it wouldn't be completely improbable.

For safety, I would definitely run the RootKit revealer (from sysinternals), MBAM, your own AV scanner (Avast) while in safe mode and preferably with this hard drive slaved into another system.

But based on AV behavior I have observed myself, I think it is more likely this was a system driver failure that resulted in a restart rather than a virus.

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This sounds plausible indeed. There was nothing out of the ordinary in my logs, and it was right after Avast turned itself off, the system rebooted. I am however running some different scans. They have revealed nothing yet. – Simon Verbeke Jun 30 '11 at 16:18

See my post here

Use the link in the EDIT section, make the Microsoft System Sweeper boot CD or usb thumbdrive, boot from it and scan the system, normal scanners inside Windows may not find the latest generations Malware Rootkits.

Yes you can be rooted just by visiting a malicious website.

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I got the same message about Avast being turned off in the action center, yet Avast itself said it was on and secured.

Right-click the Avast taskbar icon and go to "avast! shields control" > "disable for 10 minutes" then click yes in the pop-up window.

Go back to the taskbar icon menu "avast! shields control" > "Enable all shields." The action center alert should go away.

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When Windows shows my Avast a/v turned off and does not respond to my turn it back on! I go to control panel - uninstall/change - in uninstall - click REPAIR. You may have to repeat the proccess once more before the Windows X Flag is removed and the orange Avast Orb starts spinning to show it is once again activated.

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I had too rootkits and did not know it,funny thing was showed avast working,but then it would disappear,so I just tried malwarebytes,did a hyper scan,it found both,now am saying malwarebytes is the best,never had this before ,so must of had it for some time,got to be careful which sites you go too,then run scans ,have two firewalls but they got threw,now it works great,and because don't have lots of files i watch them

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