One of the first reported cases of plant floor “hacking” occurred in 1988 on an Allen-Bradley DH+, which was used by an angry worker to modify a different department’s PLC-5. The individual changed the password to something obscene, blocking all maintenance access to the system. It was believed that the employee found the original password on a post-it note.

Shut down of PLC to clear memory and reload program. Loss of staff time and a brief system shutdown while resetting the password.