Patent ID: 8528054

Claim:
A method of obtaining access to an Internet service using a multi-step challenge response test, comprising: calculating a threshold probability for access to the Internet service; generating a plurality of challenge response tests, such that each challenge response test is rendered on a display of a client device, wherein at least one of the plurality of challenge response tests is a single-character, motion-enabled challenge response test; receiving an input corresponding to a response to one of the challenge response tests; calculating an authentication probability after each response, the authentication probability depending at least in part on P MOC , where P MOC is a probability that an attacking system correctly solves a challenge response test and P MOC is higher than a probability corresponding to random guessing; evaluating after each response if the authentication probability is higher than the threshold probability; providing access to the Internet service if the authentication probability is higher than the threshold probability; and increasing a number of challenge response tests rendered on the display if the authentication probability is between the threshold probability and a lower threshold probability after the plurality of challenge response tests are completed the lower threshold probability indicating that a request for access to the Internet service is being made by an attacking system.