How are viruses & malware spread in today's world

They are mainly transmitted through weak operating systems that allow a site or an email into an area on the computer that can then be altered. Once this happens they can then disable your firewall and have access to your passwords etc. A good operating system (read NOT Microsoft) can make this very difficult. I can't count how many years I have been running without being infected. BTW I don't even use an anti virus program.