VirtualBox is software that simulates a computer's physical hardware. You can install any operating system you want onto it. People often install windows onto it, then install new untrusted software to test it. Any virus in the new software theoretically remains safely quarantined in virtualbox's simulated computer, although there are some caveats.
If you intend to use virtualbox for virus protection first research how to configure it, and check out all its caveats.