My company uses a web filtering software from an unknown (to me) vendor. I noticed the other day that YouTube automatically defaults to "safety mode" and that I am unable to change this setting. Instead, YouTube displays the message
SafetyMode is enabled by your network administrator
I assume the filtering software is setting the flag, but how is it enabled? I've looked through Google's help pages, but I didn't find anything about this. I'm asking mostly out of curiousity, because I have never seen a website prevent a visitor from doing something due to a network policy on the client side.