http://www.gameinformer.com/b/news/archive/2011/06/05/nintendo-servers-hacked.aspx
It was a hacking attempt by a group called LulzSecurity. Looks like they apparently wanted to help Nintendo by spotting a loophole and telling them to fix it. "We're not targeting Nintendo. We like the N64 too much - we sincerely hope Nintendo plugs the gap. This is just for lulz.
