What kind of screwdriver can unscrew this?
Solution 1:
Looks like a "Tamper-Resistant Torx" screw, according to http://resources.tannerbolt.com/articles/what-type-of-screw-is-this/ . Another name is "Torx Security" screws. I get some good results on Amazon for Tamper Proof screws too.
Test what size was closest (diagonal fit) to get the approximate size you need. Probably the best action is to buy a whole set of interchangeable heads for your screwdriver.