The U.S. Patent & Trademark Office has invalidated for the second time a design patent that Crocs has been using for its iconic clog, this time supporting a challenge made by U.S.A. Dawgs, a shoe company based in Las Vegas, which was importing similar strapped clogs from competitors. Often referred to as “the ‘789 patent,” the U.S. patent bears the number D 517,789. It was issued to Crocs' founder, Scott Seamans, in 2006. The patent office noted that Crocs had featured the clog's design in its own website more than one year before it applied for the patent. The U.S. District Court of Colorado is still examining  another claim with regard to a utility patent, No. 6,993,858, issued to Crocs for its clogs. Crocs had sued Dawgs for infringement of both patents in 2006.