There are lots of faults. The software failed. The process that directed a helpdesk tech to install AV was a failure of some manager. The decision to engineer systems and networks in a way such that AV seemed like a good idea was a failure of an architect.
In my opinion, the software failed because the entire system (software, hardware, and humanware) failed to implement, holistically, a safety critical system. You simply cannot ignore the system as a whole. I'd wager we are in violent agreement. :)
