The smallest virus was only 19 bytes long. Yeah, those zipped viruses in emails are real dumb. But they still work. It's social engineering that is doing the trick. Click here unless you want to be doomed! People believe it. They also believe a lot of other crap TV tells them, so no surprise.
BTW a firewall surely gives you some kind of control. Unlike hardware firewalls some software solutions will not only block unwanted protocols etc, but also tell you when an application is trying to "phone home" and THAT will tell you a lot. But of course, a good antivirus app is required. I'd suggest to use a resident Guard that prevents even the very first execution of known viruses.
BTW a firewall surely gives you some kind of control. Unlike hardware firewalls some software solutions will not only block unwanted protocols etc, but also tell you when an application is trying to "phone home" and THAT will tell you a lot. But of course, a good antivirus app is required. I'd suggest to use a resident Guard that prevents even the very first execution of known viruses.