WTF just happened?

I was playing online with my dad today in private party mode, and, as usual, I was PWNIN my dad. Then out of nowhere this random guy, not on my friends list, joins. So my dad says to me, "Who the **** is that?" and I said to my dad, "I don't know." He kills himself a couple of times, I kill him once, and then he leaves the match. Has anyone else had this happen to them. And by this I mean, some random guy coming into your private match?

no but people on the wii sometimes joins the match when the party is already full and they start hacking it on the wii

I've had this happen on Need for Speed; Shift. Problem I had was that even though I had created a 'private' match for myself and my friend. I hadn't changed one of the settings that limited it only to invited people or something. It was 'private' match only in the sense it wasn't the same as public, open matches or something. I don't know what its like for W@W but maybe you didn't change one of the settings or something? lol I don't know, just spit balling ideas

You can change the settings between private (only available to friends), or closed (no more people can join) ZOMG!