Chromebooks are pretty resistant to most viruses and trojans, but that isn’t foolproof. To avoid malicious software, make sure you do these two things:
- Do not put it into developer mode. That removes the security built into the hardware and allows any software to run on the computer.
- Be very careful what Chrome extensions you install. Stick to the reputable ones.
When you get a new Chromebook, it may be setup more for convenience than security. For example, you might log in, then leave it, and an hour later someone else opens it up and starts sending emails as you. That's not great. Update the settings to make more secure defaults.