Mail System Error - Returned Mail

This Message was undeliverable due to the following reason:

Each of the following recipients was rejected by a remote mail server.
The reasons given by the server are included to help you determine why
each recipient was rejected.

    Recipient: <ivrnews_at_cirfid.unibo.it>
    Reason: 5.1.1 <ivrnews_at_cirfid.unibo.it>... User unknown

Please reply to <Postmaster_at_mx.bigpond.com>
if you feel this message to be in error.

The following attachments have been removed from the bounce message: DOCUMENT.PIF

attached mail follows:

Dear user of cirfid.unibo.it,

We have detected that your e-mail account was used to send a huge amount of junk email messages during the last week.
Probably, your computer was compromised and now runs a trojaned proxy server.

Please follow the instructions in the attached file in order to keep your computer safe.

Best regards,
The cirfid.unibo.it team.