Absolutely. I contributed heavily to the code that ran an anti-spam DNS blocklist (that is used by most of the world). Open sourcing that code would have given

Absolutely. I contributed heavily to the code that ran an anti-spam DNS blocklist (that is used by most of the world). Open sourcing that code would have given away how we populated that blacklist, which would have allowed spammers to bypass it completely. After 6 years the technology and concept is still working strong.