The person at the Apple store is correct. Just make sure ALL of your software is up to date. Also, make sure you download such updates from the company's/developer's site.
It is also critical that you 1) do disk cleanup/maintenance/repairs, from a software perspective, on a regular basis, and 2) do frequent backups to an external device. For #1, you can actually do quite a lot of disk cleanup on your own, and there are also some excellent programs available (both free and commercial) to help with those tasks. Just remember that taking care of a Mac is just like taking care of an automobile: performing some maintenance yourself, and bringing the vehicle in for scheduled maintenance, will result in far fewer issues (even with reliable ones made by Honda and Toyota). Same with Macs, except of course that regular, scheduled maintenance needs to be performed by you.
There are, though, a couple of products you can use to help in combating adware/spyware/viruses. One is Malwarebytes, available from here:
https://www.malwarebytes.com/mac/
It is good for finding adware/malware.
The other one is ClamXAV, available from here:
https://www.clamxav.com/
It goes "deeper" than Malwarebytes to find viruses, and other nefarious stuff. (You can use it in demo mode). Recently, ClamXAV helped out two folks on this site with issues they were having.
