Problem 1: Is it ethical for you to hire away from your competitor a secretary who may have overheard something that will be useful to you?
Problem 2: Is it ethical for you to send an attractive employee to a bar where your competitor's programmers hang out in the hope of getting the information you want?
Problem 3: Is it ethical for you to have someone hunt up and read everything published by your competitor's programmers in case they may have let slip something that will help you?