4x4x4 Cube Puzzle

4x4x4 cubes can be formed using eight different solid heptominoes. In the middle 2x2x2=8 places are free. In the following applet 100 solutions are provided.
The pieces can be moved by drag and drop. First you must choose a single cube and then drag it onto another one or a square of the plane.
If the computer is forbidden to rotate the pieces the task is rather easy, otherwise it's difficult. In this case you can rotate the heptominoes clicking onto a face of a cube. The heptomino will rotate around an axis perpendicular to the chosen face.