For several months, I had been getting mysterious instant messages from strangers. Somebody with an unfamiliar username ending in -coho would IM me "hey" or "who's this" or some bit of nonsense. I would typically answer "Do I know you?" or "Who's this?" Then the other person would answer: "What are you talking about? You IM'd me!" They turned out to be as equally baffled and suspicious as I was.