Malware
Trojan horses are a type of harmful software that masquerades as a regular, benign program or utility in order to persuade a victim to install it. A Trojan horse usually carries a hidden destructive function that is activated when the application is started. They need a user to agree to run a program to work and cannot copy themselves from one computer to another. However, trojan horses can make the same problems a normal virus can make. They can also allow the malware writer to control the victim's computer, install more malware, steal bank data, and more. For example, ransomware is a type of trojan horse that stops a victim from using their files until they pay the person who wrote the malware. Experts think that trojan horses are the most common type of malware in existence.