Odds are that someone who has your address in their address book has the virus.
Many mass-mailing viruses steal addresses from a hosts mail program and send
itself to everyone in the list.
Never fear, most viruses come as an attached file. If you don't recognize the
sender or the file, don't open it and don't auto-execute any files. So long as
you don't, you won't get the virus.
Your having a Mac further decreases the possibility that you have a virus on
your system.