Chromebooks and Chromeboxes don’t really need Anti-Virus in the same way that Windows and MacOS do. The ChromeOS system is based on a Linux kernel and is written in such a way that it does not allow other programs to run other than the ones it knows about – ie the programs which are part of the operating system.
That said, you should still be very cautious of phishing email and malicious websites which will attempt to trick you in to entering your personal data.
Make sure you have a long, non-dictionary based password with UPPERCASE, lowercase, numbers and special characters;
(Muddle-Berry-Wash19) is a good example of a 21 character password using all the character classes.
Finally be careful of Chrome browser Extensions – some Extensions grant access to your Google Docs, Gmail and other personal data held by Google, sometimes for legitimate reasons (eg a mail merge Extension for Gmail and Google Drive) but there are evil-developers who write Extensions with exciting sounding names in order to entice you, and then capture your personal details.
Hope the above proves useful.