Instead of randomly spreading from computer to computer by riding along with e-mail or on a floppy disk, it intentionally sent itself to all your friends. Certainly Melissa was a terrible waste of time and money, costing corporations and individuals billions of dollars in lost time while they fixed their computers. But it was also proof that marketing has changed forever. Because the virus spread itself through millions of mininetworks of people who trust each other and talk to each other. When these mininetworks work properly, they spread information at the speed of light.
People use the Internet primarily to talk to each other.
And more often than not, they're talking to each other about things that get marketed. They talk about rock groups and airlines and stock offerings and restaurants and religions. When the company upgraded MSN this fall, the upgrade process included a box customers could check to let their friends know they'd upgraded and invite them to try the new product. Without asking each time. You were Microsoft's marketing strategy, whether you wanted to be or not.