Typically, tamper seals that are identifiable as broken are placed on all access doors (including the power switch, data load slots, etc), access panels, and openings on the device. All seals were verified in tact before and after the election, and no voter was ever permitted in the back of the access panel where the firmware update would take place.
Before the machine starts, it gives a "zero" report which is verified independently by poll watchers, and confirms candidate choices are in place as needed. When the polls are closed, we seal everything again before the machines are sent back for reporting (at which point the seals are checked and verified prior to dumping results).
If this was really a damaging hack, the protective counter & live counters would show different numbers than what the machine read, but that didn't happen. It very clearly was tampered with, which means these physical measures would counteract any unwanted firmware updates during an election. It's preposterous to think that election judges aren't actively verifying seals during election day and making sure nobody is tampering with them.