Viruses, Trojan Horses, Spyware
The malware trojan horse, much like the orignal Greek one, opens a back door to your computer. When you open or download a program it could be secretly attached. Even if your download seems normal and fine. It accesses other applications on your computer. It doesn't spread like a virus
A virus can ruin your computer. There are different types of viruses and they attack different parts of your computer. Some attack your hard drive. The only point of a virus is to spread. It can access your contacts and send itself to everyone you know. They are usually passed through an email. Now they are sometimes attached to texts and even flash drives.
How You can Avoid Malware
Use common sense
Don't open email attachments from unknown senders
Always use AntiVirus software
Put up a fire wall