Here is the answer right from the Microsoft Gods.
"Microsoft states: 'If you continue to use Windows XP or use Windows XP Mode on a Windows 7 PC after support ends, your PC might become more vulnerable to security risks and viruses.'
"So, is XP in a VPC or XP Mode safe? Or is it as vulnerable as a standalone XP system?"
When Microsoft drops support for XP, all XP PCs — real or virtual — will become equally vulnerable to newly exploited security flaws.
I'll say that again. XP running in any virtual PC software — XP Mode, VirtualBox, VMware, Hyper-V, or whatnot — will be just as vulnerable as a real, standalone XP machine.
There is, however, a significant upside to running XP in a virtual machine. The software that creates and manages virtual systems typically protects the host PC from any corruption or infection of the XP VPC (or any other guest OS). The host system is effectively isolated from whatever software is running inside a VPC. That rule, of course, is not absolute; the level of protection depends on how the VPC is set up. But security problems that might affect a virtual PC usually can't migrate to or otherwise affect the host PC.
BACK to me again.
The fact is, a virtual PC can be a good way to run any potentially hazardous software. System crashes, bugs, hacks, or other problems that might affect the guest operating system won't, in most cases, affect the host (physical) system.