Most anti-virus products rely primarily on signatures to stop viruses. These signatures are based on known viruses. Relying solely on this method leaves a dangerous window between the times a virus first appears and the time a signature is developed and deployed. At the moment the outbreak occurs, Time Zero, a virus has the opportunity to do significant damage to your computer system. Every passing minute until a signature arrives is enough time for a virus to multiply exponentially and compromise another portion of your network.