When installing Microsoft Security Essentials (MSE), a validation will be performed on genuineness and legitimacy of Windows operating system. If the Windows system is not validated and deemed to be pirated, not genuine or illegal, then the Microsoft Security Essentials free anti-virus program will quit installation and cannot be installed.

However, the validation by Microsoft Security Essentials can be erroneous, and inaccurate. For example, a genuine system can be incorrectly marked as non-genuine due to validation error by the MSE, yet on other Microsoft’s validation channels, such as web validation, the system is determined to be genuine.

This issue may occur if the WGA (Windows Genuine Advantage) engine does not have permission to access the data.dat file. Follow the steps below in order (for Windows XP as problem so far been limited to Windows XP system) to verify and confirm that it’s invalid data.dat permission that cause the problem, and resolve and fix the error.

  1. Log on to the computer using an Administrator user account.
  2. Click “Start”, and click “My Computer”.
  3. On the “Tools” menu, click “Folder Options”.
  4. Click the “View” tab.
  5. Under “Hidden files and folders”, check (tick) on “Show hidden files and folders”.
  6. Uncheck (untick) the “Hide extensions for known file types” check box.
  7. Click “OK”.
  8. Open Windows Explorer, and navigate to the following folder:

    %ALLUSERSPROFILE%\Application Data\Windows Genuine Advantage\data


    C:\Documents and Settings\All Users\Application Data\Windows Genuine Advantage\data

  9. Right-click the “data.dat” file, and click “Properties”.
  10. Click the “Security” tab.

    Tip: The hack to recover missing or not found Security tab in Windows XP Professional. For Windows XP Home edition, Security tab is only available in Safe Mode. So, in order to access the Security tab in XP Home Edition, restart the computer into Safe Mode. In Safe Mode, log onto Windows with accounts with Computer Administrator privileges (where only these accounts are listed on the logon screen anyway).

  11. Click on “Advanced”.
  12. In the “Name” tab, check if “Everyone” is listed.

    If “Everyone” is listed, click the “Exit” button, and check (tick) the “Full Control”.
    If “Everyone” is not listed, click the “Add” button, enter the name “Everyone” (without the quotation marks), and hit Enter. Choose “Full Control” in the pop-up window, and click “OK”.

  13. Click “OK” to accept the changes.

The error is part of the invalid non-genuine validation for Windows XP-based computers when incorrect or corrupted data.dat file is present, so that solution for the problem can be used too.