I reckon the terrorists are winning! There's a constant barage of emails, and even web pages now, pretending to be something innocent and hoping to catch me off-guard with an inadvertent click. Thank goodness I use a Mac or I might be really scared. But I do feel that my digital life (at least) is under escalating threat and I need to be ever vigilant.
The debate rages on as to whether Mac users should run anti-virus software. If the definition of a computer virus is self replicating, automatic installing code, then the answer is no because the MacOS's underlying Unix core prevents automatic installation by requiring the user to enter an administrator password for any installation. That's the very simple answer though, and we're all probably aware that we also need to be aware of, and protect against, the increasingly clever methods being employed to sneek past our vigilance.
New security breaches are constantly coming to light so it behoves us make an effort to at least generally keep abreast of what's coming over, under, or through our walls. It's comforting to know though, that Apple takes all this very seriously and is working hard to protect us.
To that end it really helps if we do our bit by installing Apple updates as soon as we can after they're released, although it's probably a good idea to let a few hundred thousand people test them before you ;-) Give it a day or so.
That said, I have several clients still running OS versions that haven't had any updates for several years and, so far, with no ill effects. It probably depends on what you do with your Mac though.