Dont just look at these type of questions as right or wrong, they can be good problem solving sessions with the interviewers. Very few people will sell out their best friend at the drop of a dime. I personally walked through the steps i would take with the person "cheating." When the interviewers wanted more they would add a new twist or more details on the situation. Roll with the punches and be honest most of us have good moral compasses, dont be afraid to take a little time and think after you are asked the question.