The video soon began to spread virally.
The cells have been virally infected.
The movie was released in 2009 and instantly launched virally throughout the LotR fan base, reaching 6 million downloads by 2010.
Once you've created a widget for whatever you are promoting, Widget Factory helps you market it virally.
Depending on what you actually sell, a "virally popular" product could crash a server or make your bandwidth charges skyrocket.