Defender scans during the day when not scheduled to do so

[Guest]

I have Windows Defender scheduled to scan overnight, but sometimes I don't
leave my PC powered up over night. In those cases, when I boot next day
Defender says "I should have run last night but didn't, so I'll run now".

I want an option to stop this because it spoils system performance.
(note: a full scan on my PC takes 1hr:15mns and scans 465,535 objects)

 

[Bill Sanderson MVP]

I would recommend that you change your scheduled scan to a quickscan. I
know this isn't a direct answer to the question, but Microsoft's
recommendation in product help is to run quickscans, and do a fullscan when
things are detected. I do full scans on "new" machines, but not routinely,
except to cover users storage on fileservers.

A quickscan looks at what is in memory, and the startup vectors, and works
outward from there--it is designed to catch in-place infections. And it is
far less resource intensive than a full scan--on office machines, I see
quickscans that take less than 2 minutes.

You can run a fullscan manually when you know you can spare the processor
cycles, or you could schedule a separate fullscan yourself, using the
scheduled tasks facility and mpcmdrun.exe.

 

[Guest]

I have Windows Defender scheduled to scan overnight, but sometimes I don't
leave my PC powered up over night. In those cases, when I boot next day
Defender says "I should have run last night but didn't, so I'll run now".

I want an option to stop this because it spoils system performance.
(note: a full scan on my PC takes 1hr:15mns and scans 465,535 objects)

 

[Guest]

I am annoyed that Microsoft has done absolutely nothing about this in two
months. If this defect isn't fixed I shall uninstall Defender and kiss it
good bye.

 

[Bill Sanderson MVP]

The scheduled scan is run by the Windows Scheduled Tasks facility. If that
is working correctly, scheduled scans should, as well.

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[Guest]

The scheduled scan is run by the Windows Scheduled Tasks facility. If that
is working correctly, scheduled scans should, as well.

Well, that's not really my problem, it's Microsoft's. But I think the task
scheduler is working ok. What should happen is that when Defender is
activated as a scheduled task it should look at the time of day and see if it
corresponds to the time it is scheduled to run. If it doesn't, Defender
should not scan.

I expect that this problem arises like this: Defender is scheduled to run at
say 1AM. I use my PC upto 00:15AM and then power it down. Next afternoon I
power it up and Defender will start scanning.

 

[Bill Sanderson MVP]

You are correct about what is happening, and it is by design, as I
understand it.

(and the scheduler isn't doing this, the app itself is.)

The workaround I would recommend is to schedule quick scans--as the product
help recommends, and only run full scans either when something is found, or
periodically manually--or you can create your own scheduled job to do a
fullscan.

Full scans are quite resource intensive. Quick scans are much less so, and
are intelligently designed to try to catch anything which is actully
running, or set to run.


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