Virus / Trjan related to SMTP

I am using Exchange 2000 server with sp3. In the morning when I logged in to the server .The server speed was very slow.I checked system drive I found 1 gb space less than previous day.
  Then I given netstat command and it was showing so many smtp connections established .when I stopped smtp service the server speed was very good as of previous day.
   How do eliminate this problem ? Is it virus attack or trojan .How do I check the lost 1 GB space .
dnitinAsked:
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JasonBighamCommented:
Check/Test for open relay.

http://www.abuse.net/relay.html

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ydirieCommented:
as far as the disk space, check bad mail folder. Also, do you have API virus software that is quarantine something.

rothmanjbCommented:
I am having the same problem, with the same version and SP of Exchange.  Trend Micro antivirus is not catching this.  The problem is a serious one.  We have had to stop SMTP because otherwise the badmail folder begins accumulating messages by the thousands per minute.  From what we can tell there is no open relay.  Help!!!  
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