Windows 10: Uninstalling old Windows Defender Definition Updates
Discus and support Uninstalling old Windows Defender Definition Updates in Windows 10 Software and Apps to solve the problem; Hi, I have over 62 Windows Definition Updates +Backup taking up over 7gb of my storage and can’t seem to clean any of them out. I understand they’re…
Discussion in ‘Windows 10 Software and Apps’ started by DanielKramer1, Jun 3, 2022.
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Uninstalling old Windows Defender Definition Updates
Hi, I have over 62 Windows Definition Updates +Backup taking up over 7gb of my storage and can’t seem to clean any of them out. I understand they’re important, but some of them are far older than they should be and I need space. Is there a way to delete them all and reinstall the latest?
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Windows Defender Definition Updates.
Thank you Elba for the prompt reply. However, there is a problem: In «Control Panel» under the «Programs and Features» page > «View Installed Updates» the » Windows Defender Definition Updates» are NOT listed. Consequently, I cannot delete/uninstall them.
The same thing happens when I use «Settings» >» Updates & Security» > «View Update History». Here the Definition Updates are all listed but I can’t uninstall them either. Any other suggestions?Thanks again, Fred
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Windows Defender Definition Updates.
You should not uninstall Windows Defender Definition updates, they are installed to protect your computer from malicious threats. Please leave them alone.
You update history will list previous definitions and updates that were installed, thats normal.
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Uninstalling old Windows Defender Definition Updates
Updating definitions in windows 10 Defender.
How come Defender doesn’t check my last definitions download and update them if they are not current? Windows 10 will notify me to run a scan but, with definitions that are always as much as a couple of days old. I know that definitions come on windows
update but that does not happen every day. I would suggest that every time you run defender that it would download definitions first just to make sure they are the most recent.
Uninstalling old Windows Defender Definition Updates
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Recently a colleague of mine asked me what happens in the file system when a malicious file is «quarantined».
The answer varies widely and as this is the «secret sauce» for many antivirus vendors, most of the time it is not overly documented how they do the voodoo they do. Seems like something that might make for a good blog or two so I sat down and did a few tests.
This post is going to cover what happened on my Windows 8 VM when I turned Windows Defender against a vicious EICAR.TXT file!
I chose to beat up on Windows Defender mostly because it is free and has a huge market share. Nothing personal.
So first things first: I grabbed the EICAR file and saved it to C:\temp.
Then I grabbed a copy of the $MFT to take a look at the this file’s record. Looks like this:
There is a lot going on in there but I just wanted to focus on a few things. If you are lost, read this.
NEXT, I turned on Windows Defender real-time protection. It was recommended.
Then a whole bunch of stuff happened.
Let’s start with $MFT record number 27152. So I quickly dumped the $MFT again and here’s what I got:
So what changed? Pretty much everything accept the $MFT record number.
The sequence number is increment by 4, indicating that there were numerous changes to the file. Specifically the rename and move to a new parent folder.
Lets take a closer look at the USNJrnl-$J to get an idea what happened:
###When I created the EICAR File and Added the EICAR string to it.###
2015-11-03 03:03:23.186 ref_num = 27152-96 eicar.txt File_Create,Close
2015-11-03 03:03:23.231 ref_num = 27152-97 eicar.txt File_Create,Data_Extend,Close
2015-11-03 03:06:48.274 ref_num = 27152-97 eicar.txt Data_Extend,Data_Truncation,Close
### This is Windows Defender Deleting the File. ###
2015-11-03 03:07:20.379 ref_num = 27152-97 eicar.txt Object_ID_Change,Close
2015-11-03 03:09:43.529 ref_num = 27152-97 eicar.txt Basic_Info_Change,Data_Overwrite,File_Delete,Close
###Since this Record Number is up for grabs, it is reused for a different file ###
2015-11-03 03:09:43.534 ref_num = 27152-98 5A7D7B64F11FF203E09434276A974A97 File_Create,Data_Extend,CloseSo in short Windows Defender deleted the original file. The MFT record number was up for grabs so it was picked up by a newly created file C:\ProgramData\Microsoft\Windows Defender\Scans\History\RemCheck\5A7D7B64F11FF203E09434276A974A97
So where did my EICAR file go? Windows Defender puts quarantined files C:\ProgramData\Microsoft\Windows Defender\Quarantine\ResourceData\. Mine was saved C:\ProgramData\Microsoft\Windows Defender\Quarantine\ResourceData\50\50761523FA79FDF68E04707959836D1F6DBA9969.
Let’s take a look at that:
For those that don’t know, Windows Defender and Microsoft Security Essentials Quarantine files have a magic number of 0B AD 00. Clever.
Looking at the histogram of the data, it is pretty obvious that it was stored using some kind of encryption.
After doing a bit more digging, it turns out that Windows Defender uses a hard coded RC4 key to encrypt quarantine files.
A colleague of my pointed me at the this cool script from Cuckoo
Here is the relevant chuck of their code that I bastardized for this blog post:
# Copyright (C) 2015 KillerInstinct, Optiv, Inc. (brad.spengler@optiv.com)
# This file is part of Cuckoo Sandbox - http://www.cuckoosandbox.org
# See the file 'docs/LICENSE' for copying permission.
import os
import struct
import hashlib
from binascii import crc32
def mse_ksa():
# hardcoded key obtained from mpengine.dll
key = [0x1E, 0x87, 0x78, 0x1B, 0x8D, 0xBA, 0xA8, 0x44, 0xCE, 0x69,
0x70, 0x2C, 0x0C, 0x78, 0xB7, 0x86, 0xA3, 0xF6, 0x23, 0xB7,
0x38, 0xF5, 0xED, 0xF9, 0xAF, 0x83, 0x53, 0x0F, 0xB3, 0xFC,
0x54, 0xFA, 0xA2, 0x1E, 0xB9, 0xCF, 0x13, 0x31, 0xFD, 0x0F,
0x0D, 0xA9, 0x54, 0xF6, 0x87, 0xCB, 0x9E, 0x18, 0x27, 0x96,
0x97, 0x90, 0x0E, 0x53, 0xFB, 0x31, 0x7C, 0x9C, 0xBC, 0xE4,
0x8E, 0x23, 0xD0, 0x53, 0x71, 0xEC, 0xC1, 0x59, 0x51, 0xB8,
0xF3, 0x64, 0x9D, 0x7C, 0xA3, 0x3E, 0xD6, 0x8D, 0xC9, 0x04,
0x7E, 0x82, 0xC9, 0xBA, 0xAD, 0x97, 0x99, 0xD0, 0xD4, 0x58,
0xCB, 0x84, 0x7C, 0xA9, 0xFF, 0xBE, 0x3C, 0x8A, 0x77, 0x52,
0x33, 0x55, 0x7D, 0xDE, 0x13, 0xA8, 0xB1, 0x40, 0x87, 0xCC,
0x1B, 0xC8, 0xF1, 0x0F, 0x6E, 0xCD, 0xD0, 0x83, 0xA9, 0x59,
0xCF, 0xF8, 0x4A, 0x9D, 0x1D, 0x50, 0x75, 0x5E, 0x3E, 0x19,
0x18, 0x18, 0xAF, 0x23, 0xE2, 0x29, 0x35, 0x58, 0x76, 0x6D,
0x2C, 0x07, 0xE2, 0x57, 0x12, 0xB2, 0xCA, 0x0B, 0x53, 0x5E,
0xD8, 0xF6, 0xC5, 0x6C, 0xE7, 0x3D, 0x24, 0xBD, 0xD0, 0x29,
0x17, 0x71, 0x86, 0x1A, 0x54, 0xB4, 0xC2, 0x85, 0xA9, 0xA3,
0xDB, 0x7A, 0xCA, 0x6D, 0x22, 0x4A, 0xEA, 0xCD, 0x62, 0x1D,
0xB9, 0xF2, 0xA2, 0x2E, 0xD1, 0xE9, 0xE1, 0x1D, 0x75, 0xBE,
0xD7, 0xDC, 0x0E, 0xCB, 0x0A, 0x8E, 0x68, 0xA2, 0xFF, 0x12,
0x63, 0x40, 0x8D, 0xC8, 0x08, 0xDF, 0xFD, 0x16, 0x4B, 0x11,
0x67, 0x74, 0xCD, 0x0B, 0x9B, 0x8D, 0x05, 0x41, 0x1E, 0xD6,
0x26, 0x2E, 0x42, 0x9B, 0xA4, 0x95, 0x67, 0x6B, 0x83, 0x98,
0xDB, 0x2F, 0x35, 0xD3, 0xC1, 0xB9, 0xCE, 0xD5, 0x26, 0x36,
0xF2, 0x76, 0x5E, 0x1A, 0x95, 0xCB, 0x7C, 0xA4, 0xC3, 0xDD,
0xAB, 0xDD, 0xBF, 0xF3, 0x82, 0x53
]
sbox = range(256)
j = 0
for i in range(256):
j = (j + sbox[i] + key[i]) % 256
tmp = sbox[i]
sbox[i] = sbox[j]
sbox[j] = tmp
return sbox
def rc4_decrypt(sbox, data):
out = bytearray(len(data))
i = 0
j = 0
for k in range(len(data)):
i = (i + 1) % 256
j = (j + sbox[i]) % 256
tmp = sbox[i]
sbox[i] = sbox[j]
sbox[j] = tmp
val = sbox[(sbox[i] + sbox[j]) % 256]
out[k] = val ^ data[k]
return out
def mse_unquarantine(f):
with open(f, "rb") as quarfile:
data = bytearray(quarfile.read())
fsize = len(data)
if fsize < 12 or data[0] != 0x0B or data[1] != 0xad or data[2] != 0x00:
return None
sbox = mse_ksa()
outdata = rc4_decrypt(sbox, data)
#prints
with open("unquar-with-meta.bin", "wb") as f:
f.write(outdata)
# MSE stores metadata like the original filename in a separate file,
# so due to our existing interface, we can't restore the original name
# from just the ResourceData file. Later we may allow uploading pairs
# of files, match them up by name, and then associate that data here
# for the final submission
headerlen = 0x28 + struct.unpack("<I", outdata[8:12])[0]
origlen = struct.unpack("<I", outdata[headerlen-12:headerlen-8])[0]
if origlen + headerlen = fsize:
with open("unquar.bin", "wb") as f:
f.write(outdata[headerlen:])
mse_unquarantine("50761523FA79FDF68E04707959836D1F6DBA9969")c:\ProgramData\Microsoft\Windows Defender\Definition Updates\Backup\mpengine.dll
c:\ProgramData\Microsoft\Windows Defender\Definition Updates\Default\MpEngine.dll
c:\ProgramData\Microsoft\Windows Defender\Definition Updates\{D45C13C3-59B3-4726-B82F-03461072F006}\mpengine.dll
c:\Users\All Users\Microsoft\Windows Defender\Definition Updates\Backup\mpengine.dll
c:\Users\All Users\Microsoft\Windows Defender\Definition Updates\Default\MpEngine.dll
c:\Users\All Users\Microsoft\Windows Defender\Definition Updates\{D45C13C3-59B3-4726-B82F-03461072F006}\mpengine.dll
c:\Windows\WinSxS\amd64_windows-defender-am-engine_31bf3856ad364e35_6.3.9600.16384_none_efe9bba68a38095a\MpEngine.dll</p>Looks like this:
I might dig a little deeper on this but this is all for now. Hope this helps.
Download Windows Speedup Tool to fix errors and make PC run faster
Windows Defender in Windows 11 and Windows 10 is set to automatically download and install the definition updates using Windows Update, once a day. If for some reason, your Windows Defender will not update automatically, or if you wish to download and save the definition updates in order to maybe update Windows Defender offline, on different installations of Windows 11/10, then this post will be of interest to you.
We have already seen how to download Windows Update manually. Today, we will see how you can manually update Windows Defender in Windows 11 and Windows 10. I will also give links for downloading updates for Windows Defender in the post.
First, check whether you use a 32-bit or 64-bit version of Windows 11/10. Once you know the version of Windows installed on your device, download the installers from the following links:
- Download definition updates for Windows Defender in Windows 11, Windows 10, Windows 8.1/8: 32-bit | 64-bit | ARM.
- Download definition updates for Windows Defender in Windows 7 and Windows Vista: 32-bit | 64-bit.
- Download definition updates for Microsoft Security Essentials: 32-bit | 64-bit.
Once the file has finished downloading, go to your download location and double-click the file mpam–fe.exe. Follow the prompts to install the update.
You can also update Windows Defender definitions using Windows PowerShell.
If you think some malware is preventing the installation of Windows Defender definition updates, you may want to run a scan with Microsoft Safety Scanner or for more stubborn malware, use Windows Defender Offline.
TIP: See how to update Windows offline.
Why can’t I update my Windows Defender?
Suppose you have installed some third-party antivirus tool. In that case, that security program can interfere with Microsoft Defender Antivirus, which could be why you can’t update it. In that case, you should disable any third-party security tool and then try to update the Microsoft Defender Antivirus. You can also run the Windows Update troubleshooter to find and fix issues related to virus definition updates.
How to update Defender using CMD?
To update Windows Defender or Microsoft Defender Antivirus using CMD, first, run Command Prompt as administrator and access the Windows Defender directory. After that, clear the current cache for the update, and then start the update using the following commands:
MpCmdRun.exe -removedefinitions -dynamicsignatures
MpCmdRun.exe -SignatureUpdate
These links are sure to interest you too:
- Update Windows Defender even when Automatic Windows Updates is disabled
- Windows Defender is turned off or not working
- Unable to turn on Windows Defender.
Anand Khanse is the Admin of TheWindowsClub.com, a 10-year Microsoft MVP (2006-16) & a Windows Insider MVP (2016-2022). Please read the entire post & the comments first, create a System Restore Point before making any changes to your system & be careful about any 3rd-party offers while installing freeware.
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New error, can’t remove Windows Defender backups / updates (formerly could do so, now gives following errors):
[WinError 5] Access is denied.: Command to delete C:\ProgramData\Microsoft\Windows Defender\Definition Updates\Backup\mpasbase.vdm
[WinError 5] Access is denied.: Command to delete C:\ProgramData\Microsoft\Windows Defender\Definition Updates\Backup\mpasdlta.vdm
[WinError 5] Access is denied.: Command to delete C:\ProgramData\Microsoft\Windows Defender\Definition Updates\Backup\mpavbase.vdm
[WinError 5] Access is denied.: Command to delete C:\ProgramData\Microsoft\Windows Defender\Definition Updates\Backup\mpavdlta.vdm
[WinError 5] Access is denied.: Command to delete C:\ProgramData\Microsoft\Windows Defender\Definition Updates\Backup\mpengine.dll
By Timothy Tibbettson 07/18/2023 |
It’s a well-known fact that any antivirus is only as good as its updates. Windows Defender updates daily, but should you run into a problem updating, here’s how you can update Windows Defender manually.
Updating your Windows Defender antivirus is simple, so if your updates aren’t working, see Steps 2 and 3 for workarounds to force Windows Defender updates. We’ve seen problems including viruses or malware that break Windows Defender and other antivirus programs and they aren’t always repaired correctly after clean up.
1: Update in Settings
Click on Start > Settings > Update & Security > Windows Updates.
If your status shows that you last updated today, you’re all set.
Otherwise, click on Check for updates.
If there are updates to be downloaded, you will see Updates available and a progress bar. This step should complete within minutes.
2: Run Windows Updates Troubleshooter
The Windows Update troubleshooter can find and fix problems with Windows Updates, including your definition updates.
Click on Start > Settings > Update & Security > Troubleshoot.
Click on Windows Update and then Run the troubleshooter.
Windows will next check for problems and repair them or tell you if there weren’t any found problems.
3: Update With Microsoft Official Download
You can download the latest Windows Defender definitions here on MajorGeeks.
These are executables, something no one else seems to do, so double-click the downloaded file and the latest definitions will install for you.
Additional instructions can be found on the download page.
4: Update With PowerShell
If all else has failed, there’s always PowerShell to the rescue. We’re going first to clear your cache and then try to update manually.
Press the Windows Key + X and click on Windows PowerShell (Admin)
Copy and paste the following two lines one at a time followed by pressing the Enter key:
«%ProgramFiles%Windows DefenderMpCmdRun.exe» -removedefinitions -dynamicsignatures.
«%ProgramFiles%Windows DefenderMpCmdRun.exe» -SignatureUpdate.
There are no notifications so wait until you see >> before entering the second line.
This code is repeated, and slightly different on multiple websites. The code also changed for Windows 10, so your success here is hit or miss, and you should only try this step if the other steps failed.
Similar:
What’s the Best Antivirus and Is Windows Defender Good Enough
Fix: Some Settings Are Managed by Your Organization
How to Enable Possibly Unwanted Applications Protection With Windows Defender
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Solved: Microsoft Defender Threat Service Has Stopped
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