I reallllllly can't wait until Toys R Us, Gamestop, or Pokemon.com does another Mew event. Then I'm seriously gonna get rid of every Mew I've ever received-so that I'm sure I only have legits. I wish people wouldn't hack. Insead of hacking they should just find a legit one, and clone it, and spread the clones around, instead of spreading hacks and clones of hacks around. But then again, how can we really tell what's hacked and legit nowadays unless we actually attend/recieve the official event Pokemon. It's frustrating isn't it.
Wait now that you mention it, I think it is. I just happened to be reading what the site defines as a hacked Pokemon, so that I'd be better at spotting hacks. And it mentioned that Pokemon that have an illegal location, such as Mystery Zone are hacked. Look at the Ribbon that Mew has. It says "A commemorative ribbon obtained in a Mystery Zone.