Barbara,
 
A virus cannot be introduced into your computer by opening and
reading an e-mail, but an e-mail message may invite you to download
something, sometimes by offering you something attractive like "free
information".  If you accept the invitation and download something,
that can bring a virus with it.  In fact, the download could consist
of nothing but the virus program itself.
 
Now a question for the computer experts - is it possible to design an
e-mail that automatically downloads something when the e-mail is
opened?  I don't think so, but I have heard some conflicting remarks
on this.
 
Paul M.