Systems and methods of dynamically updating CAPTCHA challenges are provided. For instance, a request to access an online resource can be received from a user device. A verification challenge can then be provided to the user device. One or more user responses to the verification challenge can be received. Each user response can correspond to an interaction by the user with an object from the plurality of objects. One or more risk assessment scores associated with the user can be determined based at least in part on the one or more user responses. The verification challenge can then be updated based at least in part on the one or more risk assessment scores and the one or more user responses.