Zero-day

A zero-day vulnerability is a new, unpatched vulnerability that can be exploited in an attack. The name "zero-day" indicates that no patch yet exists to mitigate the vulnerability being exploited. Zero-days are sometimes used in trojans, rootkits, viruses, worms and other kinds of malware to help them spread to and infect additional computers. Also spelled as "zeroday", "0day" and "0-day."

For more information about zero-day vulnerabilities, refer to the blog post Security terms explained: What does Zero Day mean?