Uh-oh, be on the lookout for some shady activity when using Pokemon X/Y's Wonder Trade feature. Here's some bad news from people much more familiar with the service than I.

...When people try to trade hacked Pokémon, they appear as bad eggs in the recipient’s game. These bad eggs cannot be released or traded away; they will keep multiplying until all of your boxes are filled. But, it gets worse. They will also delete your existing Pokémon and replace them with bad eggs. “Trade at your own risk,” warns the post.

Let's hope Nintendo jumps in and takes care of this soon. I'd hate to think that millions could potentially have their games ruined because of a few...bad...eggs.