I have a Linux installation (Ubuntu 12.04), managed not only by me. I had restricted SSH access to a user using
/usr/sbin/usermod -s /bin/false my_user
This didn't allow neither SFTP access nor console access.
However today, I found out that users with this shell, do have SFTP access and I'm very sure they didn't have access in the past.
Could there be a config change which is allowing this? Unfortunately, I can't contact any of the others guys to see if any accidental changes were made.