1. A method for mitigating network based attacks, the method comprising: receiving over a network, a request for content from a machine of a particular user; determining whether the request includes solution information associated with a bot detection problem, wherein the bot detection problem comprises a sequence of computations for the machine to solve without involvement of the particular user; blocking the request when the request includes solution information that is an incorrect solution to the bot detection problem; sending over the network to the machine in response to the request, a message comprising the bot detection problem when the request does not include solution information; and sending over the network to the machine in response to the request, said content when the request includes solution information that is a correct solution to the bot detection problem.