How to troubleshoot definition update issues for Windows Defender

Method 1: Check for updates in Windows Defender

To check for updates in Windows Defender, follow these steps:

1. Start Windows Defender if it is not already open. To do this, click Start, click Programs, and then click Windows Defender.
2. Check for new definitions. To do this, click Check for Updates Now.

Method 2: Manually install update definitions and verify Windows Update files

Microsoft delivers Windows Defender updates through Windows Update, through Automatic Updates, and through Windows Server Update Service (WSUS). In some cases, you might receive error messages because of problems with these services instead of with problems with Windows Defender. To try to determine the source of the problem, first try to manually install the update definitions. If you can manually install the update definitions, the problem is most likely caused by a Windows Update problem.

Step 1: Restart your computer if necessary

Switch back to Windows Defender and note the error code on the Home page. If the error message that you received in Windows Defender contains code 0x80240016, restart your computer. If the error message that you received in Windows Defender does not contain 0x80240016, go to Step 2.

Step 2: Manually install the update definitions

To manually install the update definitions, follow these steps:

1. Visit the Security Portal at one of the following Microsoft Web sites:
   • If you are using the English version of Windows, visit the Security Portal at the following Microsoft Web site:
     http://www.microsoft.com/security/portal/ADL.aspx
   • For more information about the Security Portal for non-English versions of Windows, click the following article number to view the article in the Microsoft Knowledge Base:
     923159 How to manually download the latest definition updates for Windows Defender
2. Follow the steps on the Web site to download and install the appropriate definition updates.
3. If you cannot install the definition updates manually or if you still receive error messages about definition updates in Windows Defender, some other things are occurring that are beyond the scope of this article. If this is the case, you might want to ask someone you know for help, or you might want to contact support.
   
   For more information about how to contact your local Microsoft subsidiary, visit the following Microsoft Web site.
   http://support.microsoft.com/contactUS/
4. If you were able to manually install the update definitions, the problem is most likely caused by a Windows Update problem. Therefore, you should continue with Step 3.

Step 3: Verify that you have all the required Windows Update files

To verify that you have all the required Windows Update files, follow these steps:

1. Open the Windows Update Web site. To do this, visit the following Microsoft Web site:
   http://www.windowsupdate.com
2. Install all the updates that are recommended. If you have problems with Windows Update, some other things are occurring that will require advanced troubleshooting. If you are not comfortable with advanced troubleshooting, you might want to ask someone you know for help, or you might want to contact support. For additional troubleshooting information and information about how to receive no-charge support if you are a home user, visit the following Microsoft Web site:
   http://go.microsoft.com/fwlink/?linkID=21608

Method 3: Advanced troubleshooting

Verify that no Windows Update, Automatic Updates, or Windows Server Update Service (WSUS) problems are occurring

Microsoft delivers Windows Defender updates through Windows Update, through Automatic Updates, and through Windows Server Update Service (WSUS). In some cases, you might receive error messages that are caused by problems with one of these services. In this case, these error messages are not related to Windows Defender itself. To troubleshoot a potential Windows Update problem, follow these steps.

Windows Vista, Windows Server 2008, Windows 7

1. Examine the Windowsupdate.log file for error messages, To view the log file, follow these steps:
   1. Click Start, type %windir%\windowsupdate.log in the Start Search box, and then press ENTER.
   2. For more information about how to read the Windowsupdate.log file, click the following article number to view the article in the Microsoft Knowledge Base:
      902093 How to read the Windowsupdate.log file
2. Visit the following Microsoft Web site:
   http://windowshelp.microsoft.com/windows/en-us/search.aspx?=&qu=%22windows+update+error%22
3. On the "Windows Help and How-to" Web page, enter the keywords that describe the problem.

Microsoft Windows 2000, Windows XP, and Windows Server 2003

1. Examine the Windowsupdate.log file for error messages, To view the log file, follow these steps:
   1. Click Start, click Run, type %windir%\windowsupdate.log in the Open box, and then press ENTER.
   2. For more information about how to read the Windowsupdate.log file, click the following article number to view the article in the Microsoft Knowledge Base:
      902093 How to read the Windowsupdate.log file
2. Visit the following Microsoft Web site:
   http://update.microsoft.com/windowsupdate/v6/troubleshoot.aspx
3. On the Options Web page, enter keywords that describe the problem.