I've kept my photo editing computer unconnected to the Internet for over a decade now. Over the years, I've heard people say again and again: "That's so old fashioned! There is no need to do that, anti-virus software is much better now. You really don't need to run two computers, that's a waste of money."
After being told that, again and again, it has usually taken about two to three months for me then to hear about a new form of computer virus which has successfully evaded the best anti-virus software, or has lain dormant for who knows how long and is now waking up at a pre-programmed date, or has been designed to exploit an unknown hole in this or that software package... and has begun to shred hard drives, or delete files at random, or is messing with the temperature monitoring of computer chips, or is re-writing files with nonsense code; and on, and on, and on.