It's a sunny late winter day, just a few degrees above zero.

这是晚冬晴朗的一天，只有零上几度。

《柯林斯英汉双解大词典》

One had to quit abruptly on a given day, going from about a pack a day to zero.

吸烟者必须从某天开始突然戒烟，从一天一包烟到再也不抽烟。

youdao

It is known as a "zero-day" vulnerability because, effectively, it has been there since the product was launched - day zero - and not even its developer had spotted it.

该漏洞被称为“零日”漏洞，因为这一漏洞自从产品推出以来就一直存在——从第“零天”开始就存在，甚至连开发人员都没有发现过。

youdao

Just as important, the platform will host exploits only for known vulnerabilities, not so-called zero day exploits--new attacks for which software companies haven't yet issued fixes.

FORBES: Technology

So-called zero-day, or newly discovered, vulnerabilities are rare.

BBC: Microsoft warns on previously unseen IE bug

Custom Trojans are as hard for signature based anti-virus to catch as the dreaded zero-day threats which exploit previously unknown vulnerabilities.

FORBES: Modern malware requires modern methodologies to block