So this isn't exactly GOOD news, but I figure I'd post here, for those that don't know. Any prize money you have received from FW because of any contest actually is taxable income and should be reported on your tax form. Actually, if you want to get technical about it, ANY contest prize, including the retail value of a t-shirt should be reported. Not that the IRS is going to go after you for $20 from the challenge, but I still thought I'd post that as a bit of a "public service announcement" for those who didn't know this.
I don't know about the rules in other countries, but you might want to check, just in case.