Torx screw probably
http://www.carbasics.co.uk/torx_1.jpg
Most manufacturers use security screws as a safety feature these days to make it difficult for users to get inside and electrocute themselves...
You can buy a set of security bits at most tool and DIY stores - You will also need a driving handle.
http://www.hobbytool.com/ProductImages/screwbits/3033.jpg
Peccavi
October 2009