This is not a virus, but a very simple trojan written with
Word macro language. As soon as you open an infected document,
it attempts to format your hard drive.
FormatC is not common at all and it does not spread. It is not
a problem and will probably never be.
F-Secure anti-virus products do not attempt to detect this trojan
and we have no plans to add detection of it.
[Analysis: Mikko Hypponen, F-Secure]