The mantra of the infosec guys is that no data is ever truly secure when attached to a network. No data. Ever. Simple as that.
But most of us need some networking and internet, lol. Reasonable security is firewall, anti-virus, anti-malware - properly configuring OS/browser/communication software - keeping on top of all patches/updates - and having physical control of your own hardware. Sounds like a lot of things to worry about, that's why Norton and Microsoft and Avast (and all the others) offer all-in-one-complete-security packages which take care of everything for your "convenience and peace of mind".
And, realistically, most of us don't have much on our computers which really needs securing. Personal photos, documents, and what-have-you, all very precious to us (perhaps even to those who know us closely) but generally worthless and mundane to the world at large. Probably all polluting the cloud anyhow.
Our network at work is isolated, no data goes in or out without passing through exhaustive scanning and logging on one controlled terminal, any attempt to bypass the security system is a gravely serious concern. Corporate espionage isn't a serious concern (although it's not lightly dismissed, either), but realistically we're in a business where integrity of data is critical so, unless strictly necessary, integrity of data isn't "compromised" by risky exposure to external networks. The office girls have internet, the guys in the basement do not.
"All opinions are not equal. Some are a very great deal more robust, sophisticated and well supported in logic and argument than others." - Douglas Adams
[/Korth]