root@host:~# curl http://get.docker.io | sh
What does the script do besides running blindly as root? Well if we take a look at their git repository, we can find this file and see inside:
# Add an user called docker and set its password as docker
RUN useradd -m -d /home/docker -p aaOLN9pfuDGV. docker
RUN sed -Ei 's/adm:x:4:/docker:x:4:docker/' /etc/group
Since Docker doesn't provide an easy method for me to contact them, I've opened a case on this matter in their Github and I guess will wait and see what the response will be.