Left button mouse click activates Search; how do you reset back to normal?

Had a virus attack which was fended off but has left the left button mouse click activating Search every time. Swapping the functions of the left & right buttons doesn’t help; uninstalling & reinstalling mouse – HID device using device manager doesn’t sort it out either. Tried control panel mouse options, but nothing there to help either. Using XP SP2; are there any standard MS options to correct this or is 3rd party software required?