The remainder of the security specs were online, and Ariel breathed a sigh of relief at the sight of them. The security in the facility was top of the line, but it was still controlled by the central computer and the security subroutines. Many corporations, understanding the potential vulnerability of their systems to invasions like the one Ariel was carrying out, had moved away from trusting their computer systems to safeguard their important installations. Advances in human-machine interface allowed human operators to take the role of central controller for a security system, plugging into the security grid and in effect "becoming" the building. They "felt" all of the input of the security sensors through a closed-circuit simsense feed, and they could "move" any of the building’s security systems as easily as raising an arm to swat a fly. Best of all, such systems were virtually impregnable to decker subversion because the human operator could recognize nuances no computer could match, and the two operating systems were largely incompatible.