I need help in here.
So I want to test some viruses or things that can affect your PC, but in a virtual computer, if you know what I mean. Can a virus can go trough the virtual PC and attack your hosting machine?
Thanks.

No, it cannot. The virus will affect the virtual machine only.

There's no actually Spyware or virus that knows you're running a virtual machine then go to your local machine?

If you can, explain me.

The virtual machine is completely separate from your host machine in a sense.

The only way that anything could come through is if you're using bridged networking between the host machine and the virtual (which allows the virus to come through the network, but is rare on VirtualBox unless there is a security flaw), or if you have shared folders through the virtual machine.

I would recommend installing a good antivirus on your host machine either way.

I learned most of this stuff from studying I.T. to get certifications etc.. but here's a good source of information if you need it: http://superuser.com/questions/29611/can-a-virus-from-a-virtualbox-vm-affect-the-host-computer

Everything is worth a Google search

Alright, Thanks Triton, Appreciate it.