The short answer to your question is unfortunately there isn't really anything that you can do to stop this from occurring although the good news is that the symptoms experienced are not a sign that your computer is infected with anything nasty. Businesses and individuals will continue to be vulnerable to these kinds of spoof e-mails until a more secure system of sending e-mails is implemented. To the best of my knowledge for the time being the best you can do is ignore the bounced e-mails and hope that the spammers soon find a new target.