Windows 7 automatically saves all the recent searches done by the users.
Some people are annoyed by this feature as the last three searches
become visible under the search box as you start typing in it. If the
computer is shared by others, you might not want others to see your past
searches. There is a way in which you can disable search history display
in Windows 7. However, you cannot disable search history display in
Windows 7 Home editions. This is due to the fact that you need to
utilize the Group Policy Editor for achieving this goal and it is not
available in the Home versions. Follow these steps to disable search
history display in Windows 7:

Enter
gpedit.msc in the search box of the
Start menu. Press Enter. This will open the Local Group Policy Editor.

Scroll down to User Configuration \ Administrative Templates \ Windows
Components \ Windows Explorer.
Double-click on
Turn
off display of recent search entries in the Windows Explorer search box
on the right hand side of the dialog box.

Select Enabled and click on the Apply button.
Click on the OK button.
Close out of the Group Policy Editor.

From now on, you won't be bothered by the display of recent search
history as you start typing into the search box.
