The title of this post sounds like a bad children's book, but unfortunately the tone of the post isn't nearly as cheerful. After many years, the time has finally come when I'm advising everyone to consider using anti-malware software on their Mac.
There's been an alarming increase in malware lately, and while the risk of infection is still vanishingly small, the malware that has started to appear is quite malicious, granting remote "root" access to the machines and potentially stealing data.
Apple has their own anti-malware tool built into the system which runs all the time (XProtect), and they've been very good about keeping it updated to catch and remove the really dangerous stuff; but there's a lot of other things that it doesn't currently catch, such as adware that can change your search engine or give you lots of popups in your web browser.
What I'm not recommending is running software like Norton Antivirus which runs in the background and monitors everything that's going on. This type of software is often confusing to the user, asking them to deny or approve everything that's happening without giving them enough information to decide whether it's a legitimate request or not. It is also notorious for causing programs to misbehave, slowing down the system, and causing general instability.
The software we currently recommend is MalwareBytes for Mac. It's currently free, and it only runs a scan when you tell it to (which you should do periodically, especially if you're downloading lots of software from the internet).
As they used to say on Hill Street Blues: "Let's be careful out there."