File scan count on external encrypted drive different to Defender

[DaveWetherill]

Hi,

I have a use case where I scan external drives with Malwarebytes and Windows Defender before attaching them to the network using a defence in depth approach.

Prior to the latest updates (Windows and Malwarebytes), when scanning the drives, the file count was the same.

Since the latest updates applied last week, the file count is different by approximately 25 files.

Could you provide guidance regarding this disparity please?

Thanks

Dave

[Malwarebytes]

***This is an automated reply***

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[exile360]

Greetings,

There are a few possibilities, however based on the description of events I would speculate that it is either a permissions issue where access permissions were modified on some of the files, preventing Malwarebytes from scanning them, or a function within Defender such as the Controlled folder access feature.

In the meantime, it may help to gather some logs to analyze what is going on with the installation:

1. Download and run the Malwarebytes Support Tool
2. Accept the EULA and click Advanced tab on the left (not Start Repair)
3. Click the Gather Logs button, and once it completes, attach the zip file it creates on your desktop to your next reply
   

I would additionally recommend doing the following as it should hopefully reveal why Malwarebytes is failing to scan some objects:

Create a Process Monitor Log:

• Download Process Monitor from here and save it to a convenient location such as your desktop or your Downloads folder
• Create a new folder on your desktop called MB by right-clicking the desktop background and hovering your mouse over New Folder and entering a name for the folder
• Double-click on Procmon.exe to run it and click Yes when prompted by User Account Control
• Agree to the terms of use to allow Process Monitor to run
• Once Process Monitor opens, click on File at the top menu and select Backing Files... and select the MB folder you created on your desktop
• Replicate the issue with Malwarebytes by performing a scan of the external drive
• Close Process Monitor
• Right-click the MB folder on your desktop containing the Process Monitor logs and hover your mouse over Send to and select Compressed (zipped) folder
• Attach the resulting ZIP file to your next reply, or if it is too large, upload it to WeTransfer.com using the option to send a file as a link and then post the link to the download in your next reply
  

Thanks

[DaveWetherill]

Hi exile360,

I have followed the processes you suggested. Here are the logs.

The file counts difference varies but in this case:

440 Malwarebytes
464 Windows Defender

Thanks

 Dave  MB_110520.zip

mbst-grab-results.zip

[exile360]

Thanks, your logs show a Symantec product installed.  If you are no longer using the Symantec product I would recommend running their removal tool found here.

With that said, the difference could also have to do with how files such as archives are counted by the two scan engines and I also know that there are certain non-executable file types which are not scanned by Malwarebytes so those two factors likely account for the difference in the number of items scanned.

[DaveWetherill]

Thanks, the Symantec product does not play well when having to run a second AV program. It was removed but apparently not fully cleaned out. Will run their removal tool thanks.

Is there an official line regarding the file count disparity between AV vendor's products? Our security team is well known for not accepting statements that aren't fully qualified.

[AdvancedSetup]

I'm sorry but there is no way to compare what is scanned or not scanned between 2 different products. That's like comparing apples and oranges.

Any reason for both products having scanned the same number of files is coincidence only

 

Edited May 11, 2020 by AdvancedSetup
updated information

[DaveWetherill]

Thanks for your response. I will raise that with our security team and hopefully they will allow us to resume processing.