Can’t prevent viruses?
Well, ultimately, you can!
So… There are a couple of different issues that I want to talk about with this question.
One is that there is no single anti-virus or anti-malware product that will absolutely catch every single virus or Trojan or other form of malware that’s out there. There just isn’t.
I have an article on that: “I run anti-virus software. Why do I sometimes still get infected?”