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RE: Malware detection
From: John Hebert <jhebert () bizdps com>
Date: Wed, 18 Jul 2012 18:26:13 +0000

From: mwamba chishimba [mailto:bamwamba () gmail com] 
Sent: Wednesday, July 18, 2012 2:11 PM
To: John Hebert
Cc: security-basics () securityfocus com
Subject: Re: Malware detection

Hi John,

Am running a linux based firewall/gateway(clearOS) which is also running as email server. Spamhaus has just blocked me 
because one of my PC's behind the firewall has a waledac >spambot. I have about 70 Users on the network and picking 
out who the culprit is will be a daunting task as you can imagine. I've started installing malwareBytes on all the 
PC's. In the >meantime I want spamhaus to delist me as pursue the offender. I have installed wireshark to help me 
monitor traffic and on my firewall I have blocked all outgoing traffic except for >http(s). 

Please advise how else I can prevent spam from leaving my network thereby avoiding being blocked by spamhaus ever 
again.

If you change your firewall to block all outgoing SMTP except from the mail server itself, any other computer won't be 
able to send spam anymore.  Once you do that, you'll be able to look at the firewall logs to see which IP is having 
SMTP connections dropped.

Will that prevent you from being blacklisted ever again?  Well, technically, if your mail server or one of the accounts 
on it were to become compromised, it could be used for spam.  Short of that, you're good to go.

I wrote up a vendor-neutral how-to for Spiceworks a little while ago that might help with your outbound firewall rules:
http://community.spiceworks.com/how_to/show/2901 - If anyone has anything to add, let me know and I'll update it.


Thank you in advance for everybody's help, greatly appreciated!

Kind Regards,


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