Inside the precision hack. How 4chan members subverted a Time.com online poll to reorder the options and spell out their own message. Partly poor application design from Time (the first version used a GET request without input validation), but I challenge anyone to design an anonymous online poll that can’t be fixed using the more sophisticated techniques 4chan eventually deployed based on HTTP proxies.
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I've recently been using this as an interview question. Start with "Whiteboard the HTML form for a simple A, B or C poll", and take it from there!