Windows Search in Windows 7 is turned on by default. If you are using other third party tools instead or you want to disable it because of security reasons, you can follow this tutorial.
Before you actually read it, I have to warn you, if you disable Windows 7 search, you will see:
1. All the search boxes in Windows will disappear, including the search boxes in Windows Explorer, the Start menu, Control Panel, the Documents library, and other libraries.
2. Programs that rely on Windows Search might not function properly.
3. Internet Explorer won't have enhanced search capabilities.