could have a virus that's sending these messages. Modern computer viruses routinely fake sender's details, and even bounced messages.
Alternatively (and slightly less likely) your email address may have been 'spoofed'. This is where emails appear to come from you, and they are bounced back to you when they fail to be delivered (or when someone uses anti-spam software to bounce suspect messages).
There's not a lot you can do, apart from contacting anyone who may have your address in their contact book and asking them to run a virus check.
If you do that, be sure to word your message dilomatically, many people are irritated by the suggestion that they may inadvertantly be sending such junk out.