Distinguish valid users from bots, OCRs and third party solvers when presenting CAPTCHA

1. A computer-implemented method of administering a CAPTCHA challenge and detecting the usage of a CAPTCHA bot or relay by a client computer, comprising, by a server device:

providing a CAPTCHA challenge to the client computer, the CAPTCHA challenge comprising an image and browser code for displaying the image, the image comprising a character string in which a first substring smaller than said character string corresponds to a solution to the CAPTCHA challenge and at least one second substring smaller than said character string corresponds to extra characters not part of the solution,

responsive to the browser code, displaying the image on the client computer wherein only the first substring is visible in the browser and the at least one second substring is hidden in the browser,

receiving a response from the client computer indicative of a solution to the CAPTCHA challenge,

comparing the response with the at least one second substring, and

determining, if the response includes the first substring and the at least one second substring, that the client computer used a CAPTCHA bot or relay.

2. The method of claim 1 wherein said CAPTCHA challenge comprises animation capability such that at any given time a varying portion of the first substring is hidden from view on the display on the client computer.

3. The method of claim 1 , further comprising evaluating at least one of: a number of form element focus events performed by the client computer, a number of mouse events performed by the client computer, and a number of keyboard events performed by the client computer.

4. The method of claim 1 , further comprising comparing the client computer's IP address with an IP address associated with said response.

5. The method of claim 1 , further comprising determining whether an iFrame exists on the client computer, and if so, determining the URL of said iFrame; and verifying the URL associated with a parent document of said iFrame.

6. A system for administering a CAPTCHA challenge and detecting the usage of a CAPTCHA bot or relay by a client computer, comprising a server device configured to perform a method comprising the steps of:

providing a CAPTCHA challenge to the client computer, the CAPTCHA challenge comprising an image and browser code for displaying the image, the image comprising a character string in which a first substring smaller than said character string corresponds to a solution to the CAPTCHA challenge and at least one second substring smaller than said character string corresponds to extra characters not part of the solution,

responsive to the browser code, displaying the image on the client computer wherein only the first substring is visible in the browser and the at least one second substring is hidden in the browser,

receiving a response from the client computer indicative of a solution to the CAPTCHA challenge,

comparing the response with the at least one second substring, and

determining, if the response includes the first substring and the at least one second substring, that the client computer used a CAPTCHA bot or relay.

7. The system of claim 6 , wherein said CAPTCHA challenge comprises animation capability such that at any given time a varying portion of the first substring is hidden from view on the display on the client computer.

8. The system of claim 6 , further comprising evaluating at least one of: a number of form element focus events performed by the client computer, a number of mouse events performed by the client computer, and a number of keyboard events performed by the client computer.

9. A computer program product for administering a CAPTCHA challenge and detecting the usage of a CAPTCHA bot or relay by a client computer comprising a non-transitory computer readable storage medium having computer readable program embodied therewith, the computer readable program comprising code for implementing a method comprising the steps of:

providing a CAPTCHA challenge to the client computer, the CAPTCHA challenge comprising an image and browser code for displaying the image, the image comprising a character string in which a first substring smaller than said character string corresponds to a solution to the CAPTCHA challenge and at least one second substring smaller than said character string corresponds to extra characters not part of the solution,

responsive to the browser code, displaying the image on the client computer wherein only the first substring is visible in the browser and the at least one second substring is hidden in the browser,

receiving a response from the client computer indicative of a solution to the CAPTCHA challenge,

comparing the response with the at least one second substring, and

determining, if the response includes the first substring and the at least one second substring, that the client computer used a CAPTCHA bot or relay.

10. The computer program product of claim 9 , wherein said CAPTCHA challenge comprises animation capability such that at any given time a varying portion of the first substring is hidden from view on the display on the client computer.

11. The computer program product of claim 9 , further comprising evaluating at least one of: a number of form element focus events performed by the client computer, a number of mouse events performed by the client computer, and a number of keyboard events performed by the client computer.