HEx, or Torx (a more 'rounded' 6 sided hole)?
There is a very common
'tamperproof torx' screwhead that sounds like this (you remove it with a
torx driver with a hole in the centre) amd a much less common tamperproof
hex. You can get tools to fit both (in the UK it's easy to find sets of
'security bits -- 30-odd 1/4" hex bits to fit those interchangeable blade
screwdrivers) that include both types.
And if you have any difficulty finding the right sizes of "security bits",
you can chisel off the post in the middle, or drill a hole in a
"regular" torx or allen to make a "security bit". (20 years ago,
"tamper-proof torx" bits were hard to come by, but used on the 5150 power
supply - but those were exposed enough to be removable with a 5WR
Vise-Grips.)