What is the most common type of no day malware?

Absolutely no day malware is a type of malware that is not yet known to the anti-virus software.  https://sakeradvantage.com/?p=1008 The most common type of zero day malware is a trojan horse.  see A trojan horse is a type of malware that disguises itself as a safe program in order to get access to a system. useful site