Do I need an antivirus on ASUSTOR NAS?

Your ASUSTOR NAS doesn't require antivirus

ASUSTOR runs an OS much like a Windows desktop PC. I've not run an antivirus on my PC for many years, aside from what's provided by Microsoft. The same goes for Linux and NAS. I've yet to encounter an issue where antivirus software was required on a home server because I'm incredibly careful about what's stored on it.

So long as you won't visit unknown websites on the enclosure or download attachments from phishing emails, you'll be absolutely fine. Just because the best ASUSTOR NAS likely won't be affected by viruses outright without human intervention doesn't mean you shouldn't be careful. Ransomware is a major concern with NAS.

When an antivirus would be helpful

If you're using your ASUSTOR NAS to download files from online sources, you're going to need to consider an antivirus, especially if it's from sources that aren't verifiable. Antivirus suites can also be helpful too. Hosting a website or backing one up would see malicious content detected before being sent to those who visit the domain.

But really, if you only use your ASUSTOR NAS with ADM 4.0 for file storage on the LAN, you'll be fine with no antivirus or a free app (like ClamAV) downloaded from App Central.