INTRODUCTION

While you are using Windows Defender, you receive a message that refers to definition updates in one of the two following circumstances:

•	When you open Windows Defender, you receive a message that states that you should check for new definitions. If this describes your situation, try Method 1.
•	When you try to check for updates in Windows Defender, you receive an error message that states that definition updates cannot be checked, downloaded, or installed. If this describes your situation, try Method 2.

See all the possible error messages.

The instructions in this article are intended for beginning computer users or those with more computer experience.

If you are a home user who is experiencing this problem on your personal computer, you can receive no-charge support by phone, chat, or e-mail (http://www.microsoft.com/protect/support/default.mspx). If you are experiencing this problem on a network computer at work, read the "Information for users on an enterprise network" section.

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RESOLUTION

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 (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 (http://support.microsoft.com/kb/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/ (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 (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 (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

1.	Examine the Windowsupdate.log file for error messages, To view the log file, follow these steps: a. Click Start, type %windir%\windowsupdate.log in the Start Search box, and then press ENTER. b. 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 (http://support.microsoft.com/kb/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 (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: a. Click Start, click Run, type %windir%\windowsupdate.log in the Open box, and then press ENTER. b. 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 (http://support.microsoft.com/kb/902093/) How to read the Windowsupdate.log file
2.	Visit the following Microsoft Web site: http://v5.windowsupdate.microsoft.com/windowsupdate/v6/troubleshoot.aspx (http://v5.windowsupdate.microsoft.com/windowsupdate/v6/troubleshoot.aspx)
3.	On the Options Web page, enter keywords that describe the problem.

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MORE INFORMATION

Detailed Symptoms

The exact error messages that might occur are listed here. Select the case that best describes your situation to continue to the correct method to use.

Case 1: You receive the following error message when you try to start Windows Defender: If this describes your situation, try Method 1.

Case 2: You receive one of the following error messages when you try to check for updates, to download updates, or to install updates from the Windows Update Web site:or or Note The error_code that is included in these messages represents the error code that you receive, and this error code might vary. The most common error codes are 0x8024402f or 0x80240016. However, you might receive a different error code, such as one of the following:

•	0x8024402c
•	0x80240022
•	0X80004002
•	0x80070422
•	0x80072efd
•	0x80070005
•	0x80072f78
•	0x80072ee2
•	0x8007001B

If this describes your situation, try Method 2.

Prevention Tips

Windows Defender has an option to automatically check for new definitions. To turn on the option to automatically check for new definitions, follow these steps:

1.	Start Windows Defender.
2.	Click Tools, and then click Options.
3.	Under Automatic scanning, click to select the Automatically scan my computer check box.
4.	Click to select the Check for updated definitions before scanning check box, and then click Save. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.

Windows Defender works with the Windows Automatic Updates feature to automatically install the latest definitions. To turn on Automatic Updates for Windows, use one of the following methods.

Windows XP and Windows Server 2003

1.	Click Start, click Run, type wuaucpl.cpl in the Open box, and then click OK.
2.	Click Automatic, and then click OK.

Windows Vista

1.	Click Start, click All Programs, and then click Windows Update.
2.	Click Change settings.
3.	Click Install updates automatically (recommended).
4.	Under Recommended updates, click to select the Include recommended updates when downloading, installing, or notifying me about updates check box, and then click OK. If you are prompted for an administrator password or for confirmation, type the password, or provide confirmation.

ADDITIONAL INFORMATION

For more information about how to troubleshoot these problems, click the following article numbers to view the articles in the Microsoft Knowledge Base: To see frequently asked questions about Windows Defender, visit the following Microsoft Web site:To see frequently asked questions about Windows Update, visit the following Microsoft Web site:Information for users on an enterprise network

You can use the step-by-step methods in this article to troubleshoot this problem on your work computer. However, if you are in a corporate environment, the network administrator might have configured the network in a manner that prevents you from downloading the definitions. Additionally, a network administrator might have deployed Microsoft Software Update Services server on the network. For example, the network might be using Software Update Service (SUS) 1.0. Windows Defender cannot receive updates from SUS 1.0. If this is the case, the network administrator must deploy Windows Server Update Services (WSUS). Definitions for Windows Defender must be offered from the WSUS server. Therefore, before you try the methods in this article at work, it is a good idea to contact the network administrator first to see whether trying to resolve this problem yourself is even possible.

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