What is defender21.exe?

This file is a part of the Microsoft Windows system. EXE is short for executable and these types of files are used on Windows computers to install or run software.

Some programs may need defender21.exe to run properly, so if this file is missing you may encounter issues when trying to launch applications or games. Often, you will get an error message that says “defender21.exe missing” that tells you which specific file needs to be restored so that the application or game can continue functioning.

To resolve these issues caused by a missing defender21.exe, read the suggestions below.

How to fix defender21.exe missing error?

If the defender21.exe missing error appears on your PC, you can use the methods below. Some are automatic, which means you can start a process to let the system automatically restore the file. Others are manual, meaning you will have to manually download defender21.exe and move it to the correct program installation folder. If you are not very experienced with digging through system files and would prefer not to, you can simply go straight to an automatic method.

Here our list of solutions to try:

• Method 1: Download defender21.exe
• Method 2: Fix the missing defender21.exe error automatically
• Method 3: Update drivers to restore missing .exe files
• Method 4: Scan your PC for malware
• Method 5: Use System File Checker (SFC)
• Method 6: Fix corrupted defender21.exe file by performing System Restore

Method 1: Download defender21.exe

This is the most straightforward approach, but it is fully manual and will require you to download the right exe file and place it in the correct folder on your PC.

Look through the list of available versions of defender21.exe then select the correct file and click “Download”. If you are unsure which one to download, read the section below or choose an automatic method.

How to choose the correct version of defender21.exe?

When looking through the list of EXE files, pay attention to whether it’s a 64-, or 32-bit file, as well as the language it uses. For 64-bit programs, use 64-bit files if they are listed above.

It’s best to choose those EXE files whose language corresponds to the language of your program, if possible. It’s also recommended to choose the latest version to ensure up-to-date functionality.

As long as you get these two parameters right, you won’t have any issues downloading the right file.

Where to place the defender21.exe file?

After you’ve downloaded the correct EXE file, place it inside the program installation folder. Alternatively, you can put the defender21.exe file within the Windows system directory.

How to register defender21.exe?

If placing the missing defender21.exe file into the proper directory doesn’t seem to solve the problem, this means you need to register it. To do so, copy your EXE file to the C:\Windows\System32 folder, then open a command prompt with administrator privileges. There, type “regsvr32 defender21.exe” and press Enter.

Method 2: Fix the missing defender21.exe error automatically

Outbyte PC Repair allows you to automatically repair EXE errors, without you having to worry about choosing the right file or registering it. The utility will not only download the correct version of defender21.exe for free and suggest the right directory to install it to but will also resolve other issues related to the defender21.exe file.

1. Download defender21.exe
2. Fix the missing defender21.exe error automatically
3. Update drivers to restore missing .exe files

Method 3: Update drivers to restore missing .exe files

Driver updates for the Windows operating system, as well as for network adapters, monitors, printers, etc., can be downloaded individually and installed from the Windows Update Center or by using specialized utilities.

Option 1 — Automatic Device Drivers Update

Outbyte Driver Updater automatically updates drivers on Windows. Routine manual driver updates are now a thing of the past. Just with a few clicks you can automatically search your system for outdated drivers and update all of them.

1. Download the Outbyte Driver Updater
2. Install the application
3. Launch the app
4. Driver Updater will scan your system for outdated and missing drivers
5. Click Update to automatically update all drivers

Option 2 — Manually Update Device Drivers

Of course, you can also choose to update your drivers yourself one by one. First you will need to look through them to find the outdated ones, then search for the updates online. Here’s how to do that:

1. Go to Taskbar's search box and type Device Manager, then select Device Manager in the search results.
2. Select a category to look at the devices' names - right-click the one that needs to be updated
3. Choose Search automatically for updated driver software
4. Select Update Driver
5. Windows might not be able to find the new driver automatically. In this case, you can find the driver on the manufacturer's website, where all the necessary instructions are available. Just make sure to find the official website so that you only download the trusted driver and not some malicious software.

Method 4: Scan your PC for malware to fix the defender21.exe error

Since EXE files communicate directly with your system to give instructions, they are very common targets for malware, which can intentionally corrupt these files in order to substitute them with its own malicious files. If you suspect that this is what’s causing errors on your system, you should scan your computer for malware and eliminate it as soon as possible.

Option 1 - Windows Defender

The new version of Windows 10 has a built-in application called "Windows Defender", which allows you to check your computer for viruses and remove malware. In order to use the Windows Defender offline scan, follow these steps:

1. Press the Win key or click Start and click on the gear icon to open Settings. Alternatively press Win + I key combination.
2. Select the Update and Security option and go to the Windows Defender section.
3. At the bottom of the Defender settings there is a checkbox labeled "Windows Defender Offline scan". To start it, click "Scan Now". Note that you will have to save all unsaved data before restarting your PC.

After you click the “Scan Now” button, the computer will reboot and automatically start searching for viruses and malware. Upon completion of the scan, the computer will restart, and in the notifications, you will see a report on the completed scan.

Option 2 - Outbyte AVarmor

Outbyte products are some of the most popular and effective programs for dealing with malware and unwanted programs, and they will come in handy even if you have a high-quality third-party antivirus installed. This software is specifically designed to complement your antivirus, not replace it. In the new version of Outbyte, scans can be performed in real time and manually. To initiate a manual scan please follow the steps below:

1. Launch Outbyte AVarmor and click the Scan Now button. Also, you can select the Scan option on the left side of the program’s window and click Full Scan. The system will begin scanning and you will be able to see the scan results.
2. Select items that you want to quarantine and press the “Quarantine Selected” button. After they’ve been quarantined, you may be prompted to reboot the computer.
3. After the program has been restarted, you can delete all quarantined objects by going to the appropriate section of the program. However, if you found that your system started to encounter errors after something was quarantined, you should restore the file instead.

Check your system performance to eliminate file conflicts and junk accumulation. Resolve registry and missing file errors.

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Method 5: Fix the defender21.exe missing error with System File Checker (SFC)

Many users are familiar with the sfc/scannow system file integrity check command, which automatically checks and fixes protected Windows system files. It is often one of the first things experienced Windows users do when they encounter errors.

To execute this command, you have to run Command Prompt as an administrator.

1. Start the command line as an administrator in Windows by pressing the Win key on your keyboard and typing "Command Prompt" in the search field, then - right-click on the result and select “Run as administrator”. Alternatively, you can press the Win + X key combination which will open the menu where you can select Command Prompt (Admin).
2. Type sfc / scannow while in Command Prompt and hit Enter. After entering the command, a system check will begin. It will take a while, so please be patient. Once the process is complete you will see this message: “Windows Resource Protection found corrupt files and successfully repaired them.” or “Windows Resource Protection found corrupt files but was unable to fix some of them”.

Keep in mind that System File Checker (SFC) cannot fix integrity errors for those system files that are currently being used by the operating system. To fix these files you have to run SFC command through the command prompt in the Windows recovery environment. You can get into Windows Recovery Environment from the login screen by clicking Shutdown, then holding down the Shift key while selecting Restart.

In Windows 10, you can press Win key, select Settings > Update & security > Recovery and under Advanced Startup, click Restart now. You can also boot from the installation disk or bootable USB flash drive with the Windows 10 distribution. On the installation screen select your preferred language and then select “System Restore”. After that, go to “Troubleshooting” > “Advanced Settings” > “Command Prompt”. Once in Command Prompt type the following command: sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows, where C is the partition with the installed operating system and C:\Windows, is the path to the Windows 10 folder.

This operation will take a while and it is important to wait until it is complete. When finished, close the command prompt and restart the computer as usual. You should find that the defender21.exe missing error is gone.

Method 6: Fix the corrupted defender21.exe file by performing a System Restore

System Restore is very useful if you want to fix defender21.exe error, or almost any other error. Using the "System Restore" function, you can choose to restore Windows to a date when the defender21.exe file was not damaged. Restoring Windows to an earlier date cancels changes that were made to system files since that date. Please follow the steps below to roll back Windows using System Restore and get rid of the defender21.exe error.

1. Press the Win + R keys combination to launch the Run dialog.
2. Type sfc /scannow while in Command Prompt and hit Enter.

After entering the command, a system check will begin. It will take a while, so please be patient. Once the operation is complete you will see this message: “Windows Resource Protection found corrupt files and successfully repaired them.” or “Windows Resource Protection found corrupt files but was unable to fix some of them”.

3. Type rstrui in the Run text box and click OK or hit Enter. This will open the system recovery utility.
4. The “System Restore” window may include the “Choose a different restore point” option. If so, select this option and click Next. Check the “Show more restore points” checkbox to see a complete list of dates.
5. Click the "Next" button and then click "Finish" to confirm your restore point. At this point, your computer will reboot normally and boot up with a restored version of Windows, and the defender21.exe error should be resolved.