On the one hand, it is spread via media. In details, it mainly spread thought floppy disk, light disk， hard disk or USB flash disk, and so on. Although nowadays floppy disk is not so popular and less and less people use it. In the circumstance of no internet, light disk or USB flash disk are main spread tools. Thus, you should be careful that do not use the USB flash disk and light disk which is from unknown source. Especially some pirated computer light disk.
On the other hand, it is also spread via Internet. It is no doubt that Internet is convenient and quick that is used widely in the world. However, it is another reason that why the computer is spread so fast and widely. In general, there are two approaches of network communication.
One is some malicious websites. If you visit some suspicious websites which contain malware or viruses, your computer is likely to be infected by some malware or viruses. Thus, when you visit a website, you should be careful and check whether it is official or legitimate. Do not visit suspicious or even malicious websites. The other one is email. You need to know that viruses usually hides in some email attachment, Especially in spam emails. Thus, you should be careful with some emails with attachments. And do not open the emails which are from unknown sources.
In addition, you should be careful that do not click some malicious links or pop-ups whenever you are browsing online. Choose official website if you want to download software from the Internet. All in all, you should be careful with your online activities.