Apple use pentalobe screws for their new products like the iPhone 4. The pentalobe screw is specially made to prevent users of opening their devices. It has 5 round shapes (like a flower). Apple calls it 'Pentalobular' screws. Apple protects their products this way because the pentalobe screwdrivers are not readily available. You even can't open your iPhone with a traditional Torx or Philips screwdriver. Apple's technicians have to repair defect devices with pentalobe screwdrivers. This way, Apple can protect their products without changing any design aspects of their products. Common people will not easy find a Pentalobe screwdriver even if they need one.