Why do we say “We do digital voodoo”?

Because we focus on security at the deepest darkest levels of computer systems. Specifically the areas where attackers can persist indefinitely without fear of detection, because you have zero visibility at that level.

What’s a “Legba”?

Papa Legba is the voodoo spirit that performs access control between the human world and the spirit world...or between meatspace and cyberspace.