Bounced Emails I didn't send.......

[None of the above]

Twice recently, I have received Emails purportedly sent by me and which have proved impossible to deliver. I do not recognise either the messages or the addresses to which they were sent.
Each message quotes a Hotmail account which I use regularly. I deleted the first missive without giving too much thought to it but this morning the second one arrived and I am concerned that there may be some sinister overtones. Part of the message is reproduced here:

Your file is attached.

------=_NextPart_000_0000_00003DCC.000029DB
Content-Type: application/octet-stream;
name="application.pif"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
filename="application.pif"

There then follows a substantial quantity of code.

I have run Norton Anti-virus, Ad-aware and Spybot (all up to date)
but found nothing "nasty in the woodshed".

If it is just "one of those things" I'll quite happily delete and forget, but I am worried that there may be more to it than meets the eye.

Any ideas ladies and gents?

Thanks in anticipation.