Types of Malware
Spyware is a program that secretly sends your info back to the hacker and this program sends it off so secretly you don't even know it's happening.
How to prevent this
Antivirus software is helpful because the program has a list of programs that are bad and it checks this list every time you go onto a website.
Firewalls are also helpful because when the web is trying to access you computer, or vice-versa, this firewall asks your permission.