Security with Malware or Virus in a Vbox VM?

[SubZero]

I was wondering about protection in a virtual machine with VirtualBox. I have not yet loaded Guest Additions.

If I create a virtual machine and install Windows XP in it and download a program that turns out to be Malware or have a Virus, is that program limited to inside of that one particular Virtual Machine?

Would loading Guest Additions make any difference for the security?

I mean that if I load Guest Additions does that make it so the Virus or Malware can jump from the VM to the host system and cause trouble like that?

Thank you

[Sasquatch]

Please use the search, it's been asked before. A topic like this already exists, so I'm locking this one. Use the search tip in the Forum Posting Guide to find it.