There is no conclusive answer to this question as the most common type of malware differs depending upon which region of the world you lie in, and also alters gradually. However, some of the most common kinds of malware consist of viruses, worms, Trojan horses, and adware.
Viruses are one of the earliest and most common types of malware. https://bikramyogauk.net/?p=1527 Adware is a type of malware that displays advertising on a computer system, typically in a pop-up window.
Malware is continuously evolving, and brand-new types are constantly being developed. However, the types gone over above are some of the most common that you might come across.