I taught this lesson couple of years ago and then came across this wonderful cartoon and I thought I must share this.
As much has already been written on this subject;
For a Change, I am not sharing more than 2 links of a Google Search for you:)
https://www.google.co.in/webhp?sourceid=chrome-instant&ion=1&espv=2&es_th=1&ie=UTF-8#q=what+is+legal+may+not+be+ethical