You have bad and good encryption algorythms. A good algorythm should be safe (think in i.e. pgp or asymmetrical cryptography). And that is implemented in open s

You have bad and good encryption algorythms. A good algorythm should be safe (think in i.e. pgp or asymmetrical cryptography). And that is implemented in open source means that you can verify that it is really using a good algorythm or not, and is well implemented, and don't have hidden backdoors or things like that, and if is not you because you lack the mathematical/programming knowledge to evaluate that, plenty of people that does could. In closed source you just can't verify that. And the ones with the source or that have power over them (i.e. the government) will know how safe it really is, and how get in if they want.