Microsoft Security Essentials Upgrade Error 0X80070645 Fixed

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When you are prompted to upgrade to Microsoft Security Essentials, the upgrade is not installed and you receive the error message 0x80070645. If your PC has 0x80070645, you must take immediate action against the error. 0x80070645 is not the kind of computer problem that will go away on its own. You must remove it as soon as possible to avoid further damage to your system. In most cases, 0x80070645 is a devastating computer problem that must be solved as quickly as possible.

Microsoft Security Essentials Error 0x80070645

To solve this problem, you must run one of the following solutions:

Uninstall Microsoft Security Essentials


First, you must uninstall Microsoft Security Essentials, remove all remaining registry subkeys, and then manually install the latest version of Microsoft Security Essentials.

To do this, follow the steps below.

  1. Click Start, Type or Copy and Paste Appwiz.cpl in the search box, and then press Enter.
  2. Right-click on Microsoft Security Essentials, then click Uninstall.
  3. Restart the computer.

If you were able to uninstall Microsoft Security Essentials by following the previous steps, see step 4: Reinstalling Microsoft Security Essentials. If you have not been able to uninstall Microsoft Security Essentials and some components of Microsoft Security Essentials are not uninstalled, it may not be possible to reinstall Microsoft Security Essentials.

February 2021 Update:

We now recommend using this tool for your error. Additionally, this tool fixes common computer errors, protects you against file loss, malware, hardware failures and optimizes your PC for maximum performance. You can fix your PC problems quickly and prevent others from happening with this software:

  • Step 1 : Download PC Repair & Optimizer Tool (Windows 10, 8, 7, XP, Vista – Microsoft Gold Certified).
  • Step 2 : Click “Start Scan” to find Windows registry issues that could be causing PC problems.
  • Step 3 : Click “Repair All” to fix all issues.


If you cannot uninstall Microsoft Security Essentials using Add/Remove Programs or the Programs and Features item, perform step 2: Save Registry and step 3: Remove Registry Subkeys for Microsoft Security Essentials. Step 2: Save the recording

Cleaning the Microsoft Security Essentials Trace Registry


Delete the following registry key:

HKEY_CLASSES_ROOT > Installer > UpgradeCodes >26D13F39948E1D546B0106B5539504D9

Then reinstall Microsoft Security Essentials, you may find that it is not updated the first time, but after a reboot, everything is fine.

Force Windows to restart in safe mode

safe mode

Open the advanced boot options on Windows 10 or Windows 8, if you are using one of these operating systems. Since you cannot start Windows correctly, use methods 4, 5 or 6 described in this tutorial.

On Windows 7 or Windows Vista, start the system recovery options using your installation media or a system repair floppy disk drive. Unfortunately, this process does not work on Windows XP.
Note: If you want to force or stop the start of the safe mode, and you can access Windows correctly, you do not need to follow the procedure below. See the much simpler guide to starting Windows in safe mode using the system configuration process.

After trying one of these solutions, please let us know if it has helped you in any way.

RECOMMENDED: Click here to troubleshoot Windows errors and optimize system performance