I want to add to what everyone is saying. "Security by Obscurity" is a well known security mistake, so much so that there is a Wikipedia page for it. You aren't obliged to put your code out there, but if you think that you're gaining something by keeping it secret, then:
You're not.
You're likely to be complacent about other areas of security, due to believing that this provides a layer of security.
Keeping the source secret is not a flaw in your security, but you really can't rely on it doing anything for you.
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I want to add to what everyone is saying. "Security by Obscurity" is a well known security mistake, so much so that there is a Wikipedia page for it. You aren't obliged to put your code out there, but if you think that you're gaining something by keeping it secret, then:
Keeping the source secret is not a flaw in your security, but you really can't rely on it doing anything for you.