Human attackers can use any of the hundreds of thousands of known computer exploits and attack methodologies to compromise a computer or device. The three main malware categories are viruses (self-replicating), worms, and Trojan horse programs (which require an end-user action to execute) Malware writers maintain their own malware multi-detection services, similar to Googles legitimate VirusTotal, which is then linked to an automated updating service which modifies their malware to be undetectable by current antimalware engines.”]
Source: https://www.csoonline.com/article/3267988/what-hackers-do-their-motivations-and-their-malware.html