In the context of a single system, there is no such thing as an "effective defense against 0 days" - that's marketing babble. A zero day by definition is an exploit with no defense. That's literally what that means.

That doesn't sound right.

> A zero-day exploit is a cyberattack vector that takes advantage of an unknown or unaddressed security flaw in computer software, hardware or firmware. "Zero day" refers to the fact that the software or device vendor has zero days to fix the flaw because malicious actors can already use it to access vulnerable systems.

If I never install the infected software, I'm not vulnerable, even if no one knows of its existence.

That said, you could argue that because it's a zero day and no one caught it, it can lie dormant for >2 weeks so your "just wait awhile" strategy might not work if no one catches it in that period.

But if you're a hacker, sitting on a goldmine of infected computers... do you really want to wait it out to scoop up more victims before activating it? It might be caught.