Spotlight is Mac OS X's system-wide search feature, which relies on an index of all your files to deliver rapid search results. Because each folder is indexed individually, one user can't search for files inside another user's home folder. However, all users can search files located inside their own home folders as well as files located outside the /Users folder.
If you want to prevent Spotlight from indexing any files or folders, you can exclude them from searches. For example, you might do this for files that contain sensitive information you want to avoid indexing or for files that duplicate existing content (such as backups and caches).
To exclude data from Spotlight searches, follow these steps:
Choose System Preferences to open System Preferences and then click Spotlight to open the Spotlight pane.
Click the Privacy tab, which is shown in Figure 4.16.
Click the Add (+) button, choose a folder or volume, and then click Choose to add the item to the list. Repeat this step for every item you want to exclude. Spotlight excludes it from its index immediately.
Close System Preferences.