Windows Defender warnings during scan

WilliamSB · Sep 19, 2020

Hello all!
Please forgive me in advance for what might be considered a dumb question, I'm not very computer savvy.
I'm on windows 8.1 64bit and I use windows defender with the latest definitions. I've never encountered anything during my weekly regular full scans, but lately I get a message during scan saying that preliminary scan results show that malicious or potentially unwanted software may exist on the computer. It follows by saying that detected items can be reviewed after scan has finished, but once it's over I only get the usual message that the computer is protected and that there are no found items, quarantined or otherwise.
I get this warning during every scan (only full scans though, not while scanning each disk individually), but no items are ever found. Malwarebytes found a few bloat ware-ish registry entries that were quarantined, nothing malicious, but defender still flags during scans yet ends up finding nothing.
Need I do anything more about this?
Thanks for your time.

Lacius · Sep 19, 2020

Windows Defender can have a higher rate of false positives, particularly when talking about "potentially unwanted programs." However, it's strange that you can't review the files. What happens when you go into Defender and view your history? If Malwarebytes doesn't find anything, you're probably good, but I'd want to get this figured out.

That all being said, you should update to Windows 10 at your earliest convenience. All support, including security support, for Windows 8.1 ends in 2.3 years. Windows 10 also has a lot of performance and security benefits over Windows 8.1. You can still update to Windows 10 for free, even if you missed the free update window.

WilliamSB · Sep 19, 2020

Thank you for your reply!
There is nothing in defender's history, not under "quarantine", "allowed" nor "all objects". But still, the warning shows up during every full scan, almost right at the very start of the scan.

I'm planning on getting a new computer in a while, therefore I haven't bothered with updating to 10 on this old one even though I know there might be security issues with older versions. What bothers me now though is that I don't know if it's safe to continue to do banking, email etc at this one until I get rid of that pesky warning.

Joom · Sep 19, 2020

I'm not sure if it's different from 8.1 than 10 in this regard, but do you have the option to view scan history? Not the quarantine, but the actual history. You need to find the exact files that are triggering it, and it should tell you what is. Also, use CCleaner to check your startup processes and browser extensions for anything suspicious. The "bloat" Malwarebytes removed was probably actually adware or spyware of some kind. If you're the type to just click through an installer without unchecking bundled, third-party software, you end up installing this stuff voluntarily. A lot of it ends up being difficult to get rid of as well. Most likely it's something Defender can't remove due to it being in memory, and it has a persistence stub somewhere that isn't being detected. It has an option to do a deep clean of sorts. It's an option that tells you it takes about 15 minutes to complete, so you might want to look into that.

WilliamSB · Sep 20, 2020

Thanks for the reply Joom!
I can view the defender logs in the event viewer, but there's nothing there except the regular "scan started", "scan finished", "definitions updated" and "history cleared" logs. No alerts. What MB removed was most likely something that came pre-installed on the computer when it was new, as I only download and install legit software from known sources and always check advanced install options if available to make sure no 3rd party stuff slips through. This was also the first time ever I ran MB, and defender still flags during scan even after those files were removed by MB.
I can't seem to find any option to do a deep clean (or something along those lines) in defender, the interface is limited to full, quick or custom scan and an options menu with very few options.

Joom · Sep 23, 2020

WilliamSB said:
Thanks for the reply Joom!
I can view the defender logs in the event viewer, but there's nothing there except the regular "scan started", "scan finished", "definitions updated" and "history cleared" logs. No alerts. What MB removed was most likely something that came pre-installed on the computer when it was new, as I only download and install legit software from known sources and always check advanced install options if available to make sure no 3rd party stuff slips through. This was also the first time ever I ran MB, and defender still flags during scan even after those files were removed by MB.
I can't seem to find any option to do a deep clean (or something along those lines) in defender, the interface is limited to full, quick or custom scan and an options menu with very few options.

Sorry for the late reply. It's called "Windows Defender Offline Scan". I couldn't remember it off the top of my head, and Windows seems to bury this option if you have another AV installed. You have to temporarily uninstall Malwarebytes.

Windows Defender warnings during scan

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