Comparing hiring to national demographics is not legitimate. You should compare hiring to national graduates with CS degrees, controlling for institution. That will tell you if there is discrimination in the hiring step. If you want to see if there is discrimination in entrance to CS programs, you go a step earlier, etc. And you keep walking back until you find the source of the discrepancy. Where do women get off the CS pipeline? Is it at the hiring filter? The college major filter? Somewhere in high school? Even earlier? It's disingenuous to place the blame for the entire pipeline at the feet of the entities at the very end. Somewhere there is a bias, but it isn't necessarily at the corporate level.