Corruption can begin with little things and to stay on the right track we need to know how to reject life's temptations - from greed to pride and vanity, Pope Francis said on Friday.
"Many corrupt people, many of the big fish who we read about in the papers, may have started with a small act," Francis said in a sermon as he celebrated mass at the Vatican hotel.
For example, the tradesman who fiddles the scales so that 900 grammes reads as a kilogramme," he said, quoted by Vatican Radio.
"Graft can begin with such small things, " he warned, recalling the Devil who in the guise of a serpent tricks Eve into eating the forbidden fruit in the Garden of Eden.
"The Devil is crafty and tries to trick us - he is expert in this."
Francis urged Catholics to be like Jesus, who refused every temptation by the Devil during his 40 days and nights of fasting in the Judean Desert.
"The Devil does not pay you well. He is a swindler. He promises you everything but leaves you without the clothes on your back," Francis said.