No password necessary for login to admin account

[Matthew]

Having changed the language of Ubuntu from french to english, and have set the admin to login without a password, I have added a password to the admin account. However, at the login page, I am not prompted a password when logging in.
I am prompted for one on other non admin accounts, and I am also prompted it when accessing root privileges or when the admin password is needed for other reasons on the whole of ubuntu.
I have checked and I cannot find a light.dm file with any auto-login data. I cannot understand how I can disable auto-login.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: lightdm 1.18.3-0ubuntu1.1
ProcVersionSignature: Ubuntu 4.4.0-93.116-generic 4.4.79
Uname: Linux 4.4.0-93-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: amd64
CurrentDesktop: Unity
Date: Sat Sep 2 01:19:46 2017
InstallationDate: Installed on 2016-10-07 (329 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)

[Scott Emmons (lscotte)]

Thank you for taking the time to report this issue and helping to make Ubuntu better. Examining the information you have given us, this does not appear to be a bug report so we are closing it and converting it to a question in the support tracker. We appreciate the difficulties you are facing, but it would make more sense to raise problems you are having in the support tracker at https://answers.launchpad.net/ubuntu if you are uncertain if they are bugs. For help on reporting bugs, see https://help.ubuntu.com/community/ReportingBugs.