Remember that in the secret of the Confessional you are talking to Christ Himself.
Satan
hates confession because when you reveal to Christ his lies, deceptions, and temptations, you put him to shame and Christ Himself sends him away immediately. To keep anything from the priest is to give him strength that you cannot even conceive.
Theologians say that it is highly probable that Satan can infer your thoughts anyways (and this is also the experience of the priests whose ministry is to drive away demons and who have written articles or books on the topic). Be glad to expose yourself fully to Christ by confessing even your darkest thoughts, and Satan will be defeated, for it is Christ’s own desire that “everything hidden shall be revealed”.
For your immortal soul is created by the Father pristine, in His image and likeness, saved by the sorrowful Passion of the Son, and purified by the Holy Spirit at Baptism. Any demon who has done anything to diminish your beauty and glory before God will tremble and wish that mountains would fall over them when Jesus, having heard your sincere confession, turns to look at them.
“What do you want with us, Son of God?” they shouted.
“Have you come here to torture us before the appointed time?”
"Be quiet!" Jesus said, sternly.
http://2.bp.blogspot.com/-_LGj-Eh4VtU/Tw9DBkvaMGI/AAAAAAAAABM/v1DRrp-zF_I/s240/Jesus.jpg