Solved: Protection Definition Update Failed on Windows 10

User Case 

Nowadays, more and more people are beginning to regard Windows Defender as a reliable security tool. However, it is undeniable that this plan is far from perfect. It is worth noting that in the process of using this tool, there are many errors that plague users at the same time.

Windows Defender usually receives occasional definition updates automatically on your Windows 10. One of the common problems reported by users is that an error occurs when updating this free antivirus software from Microsoft, prompting "Protection Definition Update Failed".

How to Fix Windows Defender Protection Definition Update Failed Error

In this article, we will teach you how to fix the error code that Windows Defender failed to update the protection definition. There are 5 ways to solve this problem. Therefore, it is best to try our following methods to find the one that suits you.

Note✍: In order to avoid file loss when you perform the following operations, it is recommended that you back up important files in advance.

👉 Method 1. Deleting Temporary Files
👉 Method 2. Restarting Windows Defender Service
👉 Method 3. Manually Updating Windows Defender
👉 Method 4. Running the SFC Scan via CMD
👉 Method 5. Resetting Your PC
👉 Don’t Rely Entirely on Windows Defender to Protect Your System💡
👉 What's New in Windows Update?🔥

Method 1. Deleting Temporary Files

System file damage, especially file damage related to update distribution and storage, is a fairly common phenomenon. In this case, the previous iteration of the Windows Defender virus definition may be corrupted, which may cause an error that Windows Defender will not update definitions. To solve this problem, we recommend clearing all temporary files and restarting the update process.

Tip✍: Windows Defender usually automatically updates its definitions frequently and stores them in a dedicated folder. Deleting the contents of the folder may also help.

1. In the Windows Search bar, type disk and open the Disk Cleanup tool.

2. Then select the drive you want to clean up and click OK. Here we choose the System partition (C:).

3. In the pop-up window, click Clean up system files.

4. Check the Temporary files box and click OK to clean them completely.

5. Then boot into Safe Mode and navigate to the following path and delete the content in the folder:

▶ C:\Windows\Software Distribution

6. Restart your computer and make sure that your PC is connected to the Internet. Check if the error "Protection definition update failed on Windows 10" is resolved.

Method 2. Restarting Windows Defender Service

Even though Windows Defender is a built-in tool of Windows 10, it can be disabled, and it will automatically shut down in the presence of third-party antivirus software. You can try to restart the Windows Defender service to resolve the Windows Defender updates failed error.

1. Press Win + R to open Run dialog box. Type services.msc and press Enter.

2. Navigate to the Windows Defender individual services. Right-click on each service and open the Properties of each service separately.

3. Verify that the startup type for the services is set to Automatic. If any service is stopped, start it manually.

4. Then restart your computer to see if you can perform Windows Defender protection definition update.

Method 3. Manually Updating Windows Defender

Windows Defender in Windows 10 is set to automatically download and install definition updates using Windows Update every day. If you encounter the error that protection definition update failed on Windows 10, your Windows Defender will not update automatically. Like any other program, you can manually download the latest definition of Windows 10 and install it on your computer.

1. First, check whether you are using a 32-bit or 64-bit version of Windows 10. Once you know the version of Windows installed on your device, download the installers from Microsoft website.
2. After the file download is complete, go to your download location and double-click the file mpam–fe.exe. Follow the prompts to install the update.

3. Then restart your computer. Open Windows Defender and check if the error has been fixed.

Method 4. Running the SFC Scan via CMD

As mentioned earlier, corruption of system files may cause Windows Defender Protection definition updates to fail. The SFC (System File Checker) command will scan all protected system files and repair missing or corrupted system files.

1. In the Windows Search bar, type command, right-click on the Command Prompt, and run it as administrator.

2. In the command line, type the following command and press Enter:

▶ sfc /scannow

3. Do not close this Command Prompt window until the verification is 100% complete. After everything is complete, close the window and restart your PC.

Method 5. Resetting Your PC

Finally, if you still cannot solve the problem that protection definition update failed on Windows 10 through the above methods, we recommend that you reset your PC to factory settings. It is recommended to back up your data in advance to avoid data loss caused by any unexpected circumstances.

1. Press Win + I to open the Settings app. Then select Update & Security from the menu.

2. Select Recovery in the left panel. Click on the Get Started button under the Reset this PC section.

3. Choose to Keep my files and click Next.

4. It will inform you what apps will be removed, and then explain what Reset this PC will do. Click Reset to begin the process. Wait for a while, your computer will begin to install Windows.

5. After you reset your PC to factory values, the Windows Defender updates failed error should be gone.

Don’t Rely Entirely on Windows Defender to Protect Your System

We hope the above solutions can help you. In addition to Windows Defender automatically accepting occasional definition updates, Microsoft also frequently rolls out updates to fix some bugs and issues that already exist. For example, November 2022 Patch Tuesday fixed a total of 69 Windows vulnerabilities, and 11 are rated “Critical”. You never know what will be the next vulnerability, so it is recommended to back up your computer before updating.

On the other hand, if you don't want to rely completely on Windows Defender to secure your computer, we also recommend that you use a reliable third-party free backup tool to protect your computer and files. AOMEI Backupper Standard is designed for Windows 11/10/8.1/8/7/Vista/ XP. With its help, you can:

❈ Backup system and boot partitions to an image file easily. And other hidden partitions are also backed up during the system state backup, including EFI System Partition (ESP), Recovery Partition, etc. When your computer has a system problem, you can use this system backup to restore your computer to an earlier working state.
❈ Create backup to all kinds of storage devices. Such as an external hard drive, removable USB flash drive, cloud drives, network location and NAS devices, etc.
❈ Choose 3 backup methods: full backup, incremental or differential backup. The latter two options will improve backup efficiency and further reduce the storage space occupied by image files. (Differential backup is available after upgrading to Professional edition.)
❈ Set automatic backup of your computer or files. This software helps users continuously backup data so you will never miss any changes. You can choose daily, weekly, or monthly frequency. For instance, you can backup folders to USB drive automatically.

Next, I will show you how to use this free tool to back up your system.

Step 1. Click the download button below to install AOMEI Backupper on your computer.

Step 2. Launch it and click System Backup under the Backup tab.

Tip✍: If you want to back up all the data, files and systems on your computer, you can choose Disk Backup.

Step 3. Modify the Task Name to distinguish it from other backup tasks. The program will select the system and boot partitions by default as the source, you just need to choose a destination path to save the system backup.

Step 4. Then click Start Backup to begin system backup progress.

Helpful Tips✍:
◕ Options: You are allowed to comment for system backup to distinguish it from other backups, compress the system backup image file, split large system image file into smaller ones, enable email notification to get alert after the system backup is finished, etc.
◕ Schedule: You may specify the intervals in Schedule to backup system automatically on a regular basis, such as Daily, Weekly or Monthly. (Event triggers and USB plug in are premium features in advanced editions)
◕ Scheme: You can choose backup method from full/incremental/differential backup. You can also set up rules to delete older backups automatically so that there is enough space on your backup location (only supported by paid editions).

What's New in Windows Update?

1. Windows 10 KB5034441

On January 9, 2024, Windows 10 KB5034441 was released. This update automatically applies Safe OS Dynamic Update (KB5034232) to the WinRE on a running PC to address a security vulnerability that could allow attackers to bypass BitLocker encryption by using WinRE.

2. Windows 11 23H2 Update

On October 31, 2023, Windows 11 23H2, also referred to as Windows 11 2023 Update, was released as the second significant update to the operating system. Curious about the new features and improvements introduced in the Windows 11 23H2 update? Let's delve into the details:

✌AI-Powered Digital Assistant:

• Introducing Copilot, the new AI-driven digital assistant replacing Cortana.

✌Enhanced File Explorer:

• Updated version with new visual designs, improved Gallery page, Details pane, and native support for RAR, 7z, GZ, and TAR pack file formats.
• Changes to Nearby Sharing for efficient file transfer between computers.

✌Expanded App and Tool Updates:

• Debut of Windows Backup app and a revamped Outlook email client.
• Updates across various tools like Paint, Photos, Snipping Tool, Clipchamp, Notepad, and more.

Summary

Hope you can solve the error that protection definition update failed on Windows 10 from this article. Windows Defender has always been a security tool for many users, but considering that the protection it provides is not comprehensive, it is recommended that you use third-party backup software to provide double protection for your computer.

With the help of AOMEI Backupper, you will no longer worry about data loss. If you create a system backup in advance, you can easily restore your computer to a working state when you encounter any system problems while updating to Windows 22H2, such as Windows Update 0x80080005 error. You can also use it to create bootable media to help you start your computer if it fails to start successfully. Try it now to protect your computer.