Hotmail is credited with inventing online viral marketing. I am sure there were earlier examples, but the whole point of viral is that it's so infectious that it obliterates memory of earlier attempts. I was an early Hotmail user - it was just so simple, obvious and useful.

But there is a problem with all this. I don’t believe I ever clicked on a Hotmail ad. I don’t think I even looked at them. Here is the nasty law: