If I provide a computer to an OpenERP consultant and ask him to install Linux (ex Ubuntu) and OpenERP, then, when the computer comes back, is there a way to make sure that he has not included any back doors in either Linux or OpenERP? The server would be accessible from outside the office, maybe through a VPN, also smartphones.
A back door is a way to bypass the systems that restrict access. The simplest back door is to create an extra user. Someone can then use that login. I guess looking at the user list would insure against this.