What are the security risks of using pfsense in a virtualised environment?

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http://serverfault.com – I am thinking of using pfsense on my ubuntu server box. I'd virtualise pfsense with virtualbox, and have it route and firewall all traffic on and to my server and the rest of my lan. However, I've heard that using pfsense on anything but a dedicated box poses a security risk. Why is this, and is this really an issue for a home network like mine? (HowTos)