I've never set the parental locks on my 3DS. The update from October 9th set the parental locks on my system. There was no pin, no answer for a secret question.
Not sure how many other people were hit with this little bug, but the only apparent solution is to call for a master unlock key. Nintendo's website-based unlock system didn't work for me... for some odd reason, it tells me that the serial number on my 3DS is invalid. It's odd because I bought it brand new from a Gamestop in Spokane, WA in March of 2013.