Let's face it - there are lots of nasty people out there in the ether, all hell-bent on extracting your hard-earned money from you. Most will try legal means to deceive you. For example, a Nigerian prince or other member of a royal family seeking to transfer large sums of money out of the country, and they'll give you a share just as long as you give them some bank details... legal in so far as it needs you to agree to give them the details. (By the way, if you ever consider doing this, step away from the keyboard).
Then there is the stealth kind that drops a virus on your device if you're not protected and then they can do several naughty things to you, like recording key depressions when you type the bank access code, or the password to the credit card account.
These, among other reasons, are why purchasing and installing a decent antivirus suite is an imperative. The freebies are ok, to a point, but those usually require unscheduled interaction which places the onus squarely on your shoulders to make sure the virus lists are up to date and updated, but I would always advocate investing on a full, paid-for suite - these quite often come with a lot more than just the antivirus package - for example, Norton 360 includes Anti-Spyware, Antivirus, Malware & Ransomware Protection; an area in the cloud for backing up stuff; firewall protection to prevent attacks; password manager; VPN (hides your IP address from sites that you visit); identity protection and more. And all that from £24.99 for 1 device for the first year.
Believe me, suffering a virus attack is no joke - it not only takes a lot of time and effort to ensure everything has been disinfected and that there's nothing insidious lurking in the digital shadows, but it could cost a lot as well. As I've said before (and elsewhere), it's the data you've created that needs protection, not just the installed applications.
If you're an ex-geek like me, then cleaning up someone else's problems can be fun (I even had a book dedicated to me after one grateful recipient engaged me), but do yourself a favour, don't cheap out: go buy a professional A/V package.
It's cheaper in the long run