what is the extension? It is probably an extension of either a MAC or a program someone used to make the file you downloaded that you dont have but need.
sounds like there is no extension on the file it self. Make sure to scan for a virus then rename with an extension. Use the extension that it is supposed to be and try that. You might need to use the command line to rename and add an extension.
I saw an article that said the anti p2p will be seeding the networks with large chunks of usless data to try and make the services usless. I see you figured it out but don't be surprised to find files that are just junk.