Two types of viral. 1. Artificial virality. Huge audience. Capture a part of the audience, you're in for a good userbase. Exponential increase. This is his Hot

Two types of viral. 1. Artificial virality. Huge audience. Capture a part of the audience, you're in for a good userbase. Exponential increase. This is his Hotmail example. 2. Natural virality. "John has sent you $20 over PayPal. Create an account to transfer to your bank." Built in a certain fashion that forces it to spread virally. Who wouldn't take twenty bucks?