how to force bo3 to always start offline

press your windows key and type 'windows defender firewall'
click advanced settings
click inbound rules
add a new rule, click next and then click 'this program path' and locate your bo3 executable
go to the next page then toggle 'block the connection'
add some name for the rule so you can find it later and finish
THEN
click outbound rules
add a new rule, click next and then click 'this program path' and locate your bo3 executable
go to the next page then toggle 'block the connection'
add some name for the rule so you can find it later and finish

congrats you should be safe when playing offline zombies (probably)