For as long as I have been working on Virtual PC – people have been asking me:
“Do I need to install Antivirus software inside the virtual machine?”
And the answer has always been: “Yes! You need to treat each virtual machine just like it were a separate physical computer and ensure that it is configured as securely as you would configure a physical computer.”
Because of this, I am really glad that we (Microsoft) have released Microsoft Security Essentials. Microsoft Security Essentials is a free antivirus / anti-malware / anti-spyware program that is available for Windows XP, Windows Vista and Windows 7. It is also supported inside of virtual machines – in fact the product system requirements page explicitly states that it is supported under Windows XP Mode.
You can learn more about Microsoft Security Essentials here: http://www.microsoft.com/security_essentials/default.aspx
I find this particularly useful – as I am often too lazy to bother installing a proper antivirus solution in my virtual machines, but now I do not have any excuses not to.