possible infected spam server? trying to track down what is sending out spam

I am running exchange 2003 sp2 and have barracuda spam filter filtering inbound and outbound.

pop3
imap
rpc/http is enabled

i have a situation where spam is being sent by my servers. The ip  in the headers are from a foregin country. They are somehow connecting to my email server and sending out spam.

could it be possible that one of my pop/imap users is infected with a virus and authenticating and then seding out spam?

how can i find the offending users.

I turned up loggin on pop3 and imap but do not see the offending ip anywhere.

need help in tracking down the offending user. or can it be my server has a security hole?

i am blocking the spam going outbound from the spam filter but need to get to the bottom
why its sending out.

Thanks in advance


X-ASG-Debug-ID: 1299760893-00f14f5fb10f8d0001-bDo3tZ
X-Barracuda-Envelope-From: dtglvl@tvdirectsat.tv
Received: from User ([207.194.87.105]) by server1.com with Microsoft SMTPSVC(6.0.3790.3959);
       Thu, 10 Mar 2011 07:41:33 -0500
Reply-To: dtglvl@tvdirectsat.tv
X-Barracuda-Apparent-Source-IP: 207.194.87.105
X-Barracuda-BBL-IP: 207.194.87.105
X-Barracuda-RBL-IP: 207.194.87.105
From: Online TV Software<dtglvl@tvdirectsat.tv>
Subject: Watch 9000 World Wide TV Channels on your Computer, TV or SmartPhone
Date: Thu, 10 Mar 2011 14:41:27 +0200
X-ASG-Orig-Subj: Watch 9000 World Wide TV Channels on your Computer, TV or SmartPhone