What is the ruling on dealing with leaked exam questions (aptitude test compilations) which the National Center for Assessment (Qiyas) prohibits from being leaked, but which students leak, memorize, study, and use to raise their scores?

You must adhere to the center's stated condition prohibiting the leakage of questions, based on the general evidence for the obligation to abide by contracts and conditions, as long as they do not permit what is forbidden or forbid what is permitted. This is supported by Allah's saying: ﴿O you who have believed, fulfill [all] contracts﴾ (Quran 5:1), and His saying: ﴿And fulfill [every] covenant. Indeed, the covenant will be questioned about﴾ (Quran 17:34), and the Prophet's (PBUH) saying: "Muslims are bound by their conditions."