Here are ways in which ransomware can infect your computer:

• Via email: Ransomware may be installed by downloader trojans attached to spam emails. These email messages employ various social engineering techniques to get you to open the attachment. They can pretend to be credit card bills, job applications, or documents from someone important. If you open the attachment, it installs ransomware on your computers.
• From the web: Ransomware may also be downloaded automatically when you visit certain sites. These sites contain malicious code known as exploit kits, which take advantage of outdated software to install ransomware on your computer.

This information is sourced from SPF-STAGING