This is also clearly false.
For example, take this scenario:
- You use web framework Omega, but minimise indicators of this (suppress HTTP headers, etc).
- At 2am, a critical security vulnerability is discovered for Omega and a patch is released shortly after.
- Malicious actors scrape GitHub to find sites that use Omega, and try compromise them.
- At 9am, you apply this patch.
If your project is open source, there is a 7 hour window where you are clearly and publicly broadcasting that you are vulnerable.
If your project is not, there is a 7 hour window where you are vulnerable, but this is not easily apparent to attackers.
How would you prevent this risk?