"go viral" - used in reference to Internet content which can be passed through electronic mail and social networking sites (Facebook, etc.): an image, video, or link that spreads rapidly through a population by being frequently shared with a number of individuals has 'gone viral'.
In other words, a link goes viral because most of the people who get it forward it to their Friends list or post it in their online status. Strong political content, celebrity news, news of disasters, america's funniest home videos, and crude sexual humor are popular topics to go viral.
"Dude! There was this awesome clip of this rabbit fighting a freaking rattlesnake! And winning! Did you see it? It went viral last night on youTube."
"Look, our message is important. We have to put something together that's interesting, that people connect with. Something that will go viral the instant it hits the 'Net."