1. A computer-implemented method comprising: receiving, by one or more computing devices, a request from a computing device for a webpage; determining, by at least one computing device of the one or more computing devices, a computing capability of the computing device; transmitting, by at least one computing device of the one or more computing devices, the webpage to the computing device, the webpage including one or more commands in a scripting language that are selected based at least in part on the computing capability of the computing device; receiving, by at least one computing device of the one or more computing devices, duration data representing a duration that the webpage has been open on the computing device and interaction data representing a level of user interaction with the webpage on the computing device; based at least in part on the duration data and the interaction data, transmitting, by at least one computing device of the one or more computing devices, a computational problem to the computing device; and receiving, by at least one computing device of the one or more computing devices, a result derived from processing the computational problem by the computing device according to the one or more commands in the scripting language.