Puzzle of the Week for 22 March 1999

The knight's move in chess is L-shaped: two squares in one direction, then one square in another. The black knight in the diagram attacks (can move to) any of the eight squares occupied by the white pawns.

What is the smallest number of knights needed in order to occupy or attack all 64 squares on a chessboard, and how can they be arranged in order to do this?