Well first you can't get the virus by just turning on your computer.
It gets transmitted on kazza file sharing servers. So if you're out
of town for three weeks, when you get home, before firing up kazza to
steal copyrighted material you should goto windows update and install
the updates. Windows update should be done once a week or at least
once every two weeks. That's just a fact of computing(with any os,
even linux and macs need patches). So if your gone for that long,
when you get back before you start downloading, surfing, or checking
email, goto windows update, get patched, and you're all set.
So, yes it would be your fault in the situation you describe.
What was your argument again? (Cari was right on)