Refers to a type of attack in which the sender Alice misbehaves in a way that the receiver Bob will only notice if he has a certain input. Hence, Alice learns partial information about Bob's input by observing whether he aborts. In Yao's protocol and its derivatives, Bob picks up his input for a particular wire using oblivious transfer. Alice can provide one incorrect and one correct wire label to this oblivious transfer, so that Bob picks up an invalid wire label (and eventually aborts) if and only if he has a certain input bit.