Viruses simply pull email addresses from address books and web pages to fake the sender of the email. I have even had emails supposedly from myself that contained viruses. Usually looking at the email header confirms it came from somewhere else though but the emails are usually pretty obvious fakes. Never open an attachment unless you are very sure about what it maybe. And even then I'd still run a virus check before opening it.

Never believe it really comes from the sender that it says because that can be so easily forged.