email spam or what ?

I keep on receiving unsolicited email messages on my email account that is associated with my domain on daily bases. The hacker is doing different stuff with my site.

sample of one of the emails is as shown below
Is there any one who can help us on this.

"This is an automated response sent from SalesCart

Security Error: Unable to open referring page.

Order Number: 90
Item Number: edrlcnfjzh@mydomain.com
Posted Price: edrlcnfjzh@mydomain.com
Actual Price: 0

Posting URL: http://www.mydomain.com/
Browser:
Server: www.mydomanin.com "

Can you guys help me determine what is going on?

Thanks
Dave

Then what do you suggest I do to the problem?

minimize in what sense?
Note that customer can place order sussesfuly without any problems now. Emails are sent to the customer and the merchant(both for confirmation and receipt). Does it mean that if i include this code emails are no longer going to be sent as required?
Thanks.
Dave

Thanks Techno for your prompt reponse. I still have some concerns;
Of what use is this security emails and how is it generated. It it my merchant advantage or customer advantage?

Where excertly do i put the code "<!--#include file="../cgi-bin/path.asp"-->"
thanks