A first general comment having installed a beta product you then ask about whether it has security holes, umm
The serious point here is that a VM guest will only be as protected as the OS that is running on it. So if you choose not to install / configure a firewall and anti-virus then attach it to the internet, well low and behold the machine will be infected if viruses exist to infect it.
The method of infection has implications for the safety of the host or other physical computers, an e-mail virus could infect the host etc just as it could infect the VM guest. If the VM guest uses removable media that becomes infected which is then placed in another physical computer the physical computer will become infected.
The best advice which is protect the VM guest as if it were a physical computer, hosts do not tend to get infected directly from the VM guest however with the tendency of viruses to use networking distribution there are no guarantees.
A good security ploy is to use one of the more obscure operating systems as nobody can be bothered to write viruses for them however they don't tend to be very good at playing games 