Picked up a used laptop.

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I'm convinced there is something on this computer that shouldn't be.  I believe there is 177GB of data *somewhere* on this computer that I can't account for.  I'm using windows 10 and Avast.  Avast says I'm clean.  I think I may just have a ton of temporary junk on my hard drive.  Where do I start researching this issue? Zoek?  I'm ignorant of how to best proceed.

[Eddy]

Following the instructions in the sticky at the top of this forum will be a good start.
Let's do that first.
If the system is clean, we will take it from there.

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Thanks, Eddy.  Will Do.  BRB.

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One other thing.  My user name is usert.  It came this way with the computer and I can't seem to change it to anything else.  This could *easily* be operator error (i.e. I have no idea what I'm doing) or it could be something else.  Any insights?  Logs are attached.

[Eddy]

It is late here, or perhaps I should say early.
01:55 local time

Let's see..
usert is a user account created by the previous owner (or the person who installed the OS)
It does have administrator rights (as can be seen in the log files you provided)
You can change the name through control panel, but that will only change the name and nothing else.
As they say "What's in the name? You can call a dog a cat, but that doesn't change the dog into a cat"

The MBam log shows that a PUP was detected and put in quarantine.
PUP = Potentially Unwanted Program
It doesn't mean by default it is harmful.
As the description says it is POTENTIALLY not wanted.

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[You wrote] "You can change the name through control panel, but that will only change the name and nothing else."

Yes, I gave that a shot at first and you are correct the dog stayed a dog.

[Eddy]

Hold on please before posting again.
This old dog isn't fast as he used to be, especially not at this time in the night.

[Eddy]

Ok, one step further.
Good news, the aswmbr log doesn't show any problem(s)

I'm gonna take a look at the other logs now.

[Eddy]

I have taken a look at them and there things that need to be fixed.

I can and am willing to help/guide you further, but I am not one of the "approved" malware removal helpers (as listed in https://forum.avast.com/index.php?topic=53253.0)
Simply because I never followed a "recognized" course on how to remove malware.

This means that it is up to you now to decided if you want me to continue helping/guiding you or not.
If you say "No, I will wait till one of the people in the list jump in" it is ok with me.

[REDACTED]

you sure you want to stay up any later?

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Eddy,  I'm fine with you helping me.  If you have gone to bed (which is sensible) I'll just wait for someone from the list.

[Eddy]

Awake again, well sort of 

Unless I missed something there is not really anything harmful in the log files.

Just to clean up a few things...
- Download the attached file and place it in the same folder as where you have Farbar (FRST.exe)
- Run Farbar an click on fix
- And as they say at the end of cartoons.. That's all folks.

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Hmmm.. I must have done something wrong.  Both farbar.exe and the fixlist.txt file are on my desktop yet it gives me an error when I click the fix button.  It says "Looks you don't know what to do.  To prevent damage to the system the tool will exit [sic]."

[Eddy]

Put them both in a folder and try again.

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Same problem, Eddy.