definition update for windows defender - KB915597 (1.199.1150.0)

Hi Graham,

Thank you for posting your query in Microsoft Community.

I understand that you are unable to install the update KB915597 (1.199.1150.0) and I will be happy to answer your query. Let me ask you;

1. What is the exact and complete error message?
2. Which security software is installed in the computer?

This could be caused due to various reasons. Let's try the methods below to diagnose the issue.

Method 1: If you have installed any security software, I would suggest you to disable temporarily and then check if this update gets installed.

Important: Antivirus software can help protect your computer against viruses and other security threats. In most cases, you shouldn't disable your antivirus software. If you have to temporarily disable it to install other software, you should re-enable it as soon as you're done. If you're connected to the Internet or a network while your antivirus software is disabled, your computer is vulnerable to attacks.

**Method 2:**Run the windows update troubleshooter and check.

If your computer is having problems finding and installing operating system updates, try using the Windows Update Troubleshooter to fix the problem. It makes sure that your computer is connected to the Internet, and checks to see whether your network adapter and Windows Update services are running correctly.

Method 3: I wouldsuggest you to go through the steps mentioned in the article below and check. 

You can't install updates in Windows Vista, Windows 7, Windows Server 2008, or Windows Server 2008 R2

Hope this information is helpful. Please feel free to reply in case you face any other issues with Windows in future.