Can one prevent Antimalware Executable to start hogging CPU for extended periods each time some network adapter gets active?

Unfortunately, unchecking the “Start the task only if the computer is on AC power” option won’t actually prevent the Windows Defender Scheduled Scan task from running, so it won’t really help at all. To confirm this, all you need to do is just uncheck the option, and then do a daily check of either the “Last scan” data in the Windows Defender interface – or the Task Scheduler “Last Run Result” for the scheduled scan – or this Event Viewer log (looking for the 1000 (scan started) and 1001 (scan finished) Windows Defender event IDs):

Applications and Services Logs/Microsoft/Windows/Windows Defender/Operational

So it’s very easy to prove to yourself that the scheduled scan will actually continue to run after you uncheck this option, and that the “answer” in this thread doesn’t conform to any kind of real experience with Task Scheduler. If we then grant that the answer here isn’t just a pure fabrication, we’re left with the notion that it must be based on some kind of serious misinterpretation of the Task Scheduler user interface. So let’s take a closer look at the Task Scheduler Conditions tab and see if we can’t figure out how someone might come up with the idea that unchecking the “Start the task only if the computer is on AC power” option would prevent the scheduled scan from running. If we first look at the implication of unchecking a simple instruction option, like the “Wake the computer to run this task” option, we can see that the logic is very straightforward.

Checked: Yes, Do [Wake the computer to run this task]

Unchecked: No, Don’t [Wake the computer to run this task]

Now, if the other options in the Conditions tab were simple instructions, like the “Wake the computer to run this task” option, then the meaning of unchecking them would be equally transparent. But the other options are all true “conditions”, and the logical implication of unchecking a condition option (an “only if” option) can be very murky:

Checked: Yes, Do [Start the task only if the computer is on AC power]

Unchecked: No, Don’t [Start the task only if the computer is on AC power]

At this point maybe we can appreciate how it would be easy to misinterpret the logical implication of unchecking this option as an instruction to “Not start the task if the computer is on AC power” – but that’s decidedly not the correct interpretation. When you check a condition option, you’re really asking Task Scheduler to prevent the task from running if the expressed condition (in this case; “the computer is on AC power”) isn’t met when the system state is checked prior to initializing the task. So we can just as well translate the “Start the task only if the computer is on AC power” condition into this equivalent condition: “Prevent the task from starting if the computer is on battery power” – and if we do this, I think it might help make things a little less confusing and allow us to see more clearly that the real effect of unchecking this option is simply to remove the specific restriction that’s imposed when the option is checked:

Checked: Yes, Do [Prevent the task from starting if the computer is on battery power]

Unchecked: No, Don’t [Prevent the task from starting if the computer is on battery power]

Unchecking this option simply tells Task Scheduler to lift the power-source restriction that was specified in the option – which is the same thing as telling it to ignore the option. Nowhere is there any implication that the task will be prevented from starting when this option is unchecked, and this logic is in perfect keeping with what experience teaches us, viz., that unchecking this option in fact does not prevent the Windows Defender Scheduled Scan task from running. Unchecking this option just allows the scheduled scan to run whether the computer is on AC power or on battery power – because Task Scheduler understands and follows the correct logical implications of all of the settings in the Conditions tab.

GreginMich

On the bottom right corner under selected items is a "properties". Click on that and then under conditions you should be able to uncheck power now.

You can "ungrey" enable it by clicking on the Properties link located at the right hand panel. The properties window will appear where you can do your change.

Well issue I had both processes hogging CPU and disc, but windows module installer worker was worse of two. It was not pulling 18%, but rather 40% and up. Until I went in and stopped the " windows module installer worker" service I could not do anything. Period. Hopefully this was just case of an update gone wrong or corrupted.

Wow, is this problem still not fixed? It's been like a year and a half and still nothing but angry costumers? Pathetic. Guess I won't be restarting this service any time soon...