Once this happened a third time, I saw a trend, and assumed it was not some random stalker messing with me head. Though maybe it is. (Brian, curse you!) But no, I did some research and found out it's a program called "the Great Hatsby" which originally started with a message being sent to two recipients, both of whom perceived the other as "Adjective Salmon" - saying, "I say old thing, have you seen my hat?" It just scrapes livejournal for recently updated journals, and then throws any two AIM screen-names into this conversation together.
That's far more random than the very boring "hi" that I got. Still, after realizing what was going on, I can't help but appreciate the beauty of this "spam". Really what it does is get two strangers talking, and probably reacting to something incredibly random - like being asked about one's hat. What follows is identity confusion, the sense that perhaps you aren't really you at all, and then a less-sure feeling that the world works quite exactly how you thought it did. I approve of this, basically, and think this sort of harmless GONK-inducing prank is a fine, fine thing.
By the way. Have you seen my hat, old thing? Really, I think I must have left at your place after the cotillion.