Factory reset - default passwords and security
The factory reset may well be wiping all the customisations and resetting the security - however it is probably also going to reset the access ccodes/passwords/security tokens to the original values. If the original owner did not change them (if possible) on purchasing the car then any of his/her apps that had remote access to the car would still work. For a pre-owened car with remote access to be secure REQIRES the new owner to immediately change the access codes etc or to disable the remote access (eg by removing the antenna or wrapping it in foil).