this is a very dangerous strategy. Soon or later they will know about it. At that point they could claim you tried to cheat on them, etc. In front of a judge you would have a hard time to justify such strategy. At best you may say you didn't know, but how could you prove this ? Not informing your employer and clarify the issue with them is definitely a bad strategy.

It is like walking with an armed bomb in your pocket where you could have defused it by clarifying the issue with your employer. Beside you now have the advantage of the first move. Profit from it a wisely.

So before telling anything your employer, better learn how to do it, what you are required to tell your employer, and what you can keep for your self. There are things you can't undo.