Microsoft ships the free software along with Windows Vista known as windows defender it prevents unwanted programs from running onto your pc, though removing it might not be a good idea but, if you have an antivirus then you can surely disable it. It will help you reduce the amount of system resources consumed by the Windows Vista Operating system here is how to disable/remove or uninstall windows defender
Step 1 :- Goto Start Menu > Control Panel and click the windows defender icon.
Step 2:- click on the tools menu at the top windows defender program
Step 3:- Click on the options menu
Step 4 Scroll to the bottom of the options page where you will see Use windows defender remove the tick next to it and you are done
Next you will see a notification saying that “Windows Defender is turned off”. Click on Close and you are done.