1. A non-transitory computer readable storage medium impressed with computer program instructions to enable delivering software applications including application code having one or more bonus features of an application by proximate social interaction among first devices, second devices and third devices running the application code, wherein when delivered to a device, the application code has a susceptible state and an infectious state, which computer program instructions are configured to cause a processor to: at least initiate delivering the application code that includes capability to unlock access to a locked desirable bonus feature to the first devices and second devices in a susceptible state; and at least initiate delivering the application code for the third devices either in the infectious state or triggered into the infectious state after delivery; wherein transition of the application code from the susceptible state to the infectious state is accompanied by unlocking of the locked desirable bonus feature; detecting proximate interaction of the application code running on any of the third devices with the application code running on any of the first devices; and at least initiating the application code running on respective first devices to unlock the locked desirable bonus feature and to transition the first devices from the susceptible state to the infectious state, whereby the first devices are enabled to infect the second devices and unlock the locked desirable bonus feature on the second devices.