How to find Trojan email origin

Hi everyone,

We have been getting quite a few virus "Trojan.JS.Obfuscator.aa (v)" emails lately that are caught and quarantined by the email security program called "Vipre".  I would like find out if these Trojan emails are in fact came from external IP to internal or if there is any Bot on our internal network sending these emails out.

Background:
We have a WatchGuard XCS email security appliance that acts as a gateway, filters all incoming emails before they get delivered to the Exchange server.  We have another email security program installed on the Exchange server called "Vipre" which then scans all emails for virus, spyware, spam, attachments before they get deliver to users' mailboxes.

We have received about 10 Trojan "Trojan.JS.Obfuscator.aa (v)" emails couple of days ago, all came through almost at the same time that were caught and quarantined by "Vipre".  8 of these emails were from @ups.com, 1 from @hotmail.com, 1 from @gmail.com.  The subject was either "UPS tracking number xxxx" or "United Postal Service Tracking Nr xxx". The emails were send to various internal email addresses.

Troubleshooting steps taken:
1. There was no log on the WatchGuard appliance for these Trojan emails to get any information about the origin of these emails. As per WatchGuard tech support, these emails didn't come from external SMTP address.  The log files are available for all other emails.

2. The Exchange message tracking center doesn't show any logs for these emails.  The logs are available for all other incoming and outgoing emails.

3. The Vipre email security program doesn't have any detailed logs to find origin IP or domain information.  

4. since there was no other options, I released one of these email that was quarantined from Vipre to my email address, the email header file only has the information when this email was released from Vipre, there was no previous history in the header.  somehow the previous header history is stripped out.

I am stuck at this point as I couldn't find any evidance as to whether these email came from external or internal. I am just worried if there is any Bot in our internal network sending these emails.  

Could you please let me know if there is any other way to find sender information for these emails? What do you suggest that I should do so that if it happens again I will capture more details about the email origin?


Thanks again for your help in advance. much appreciated!
BeerTimeAsked:
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David Johnson, CD, MVPOwnerCommented:
I see these in my hotmail mail all of the time that gmail will not import as it notifies me that the files are infected. I'd not worry about it.
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suriyaehnopCommented:
If you know the sender email address then you can use the message tracking to track that email since the watchguard engineer informed that the email was from external. Once trancking done, looking at client IP address
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BeerTimeAuthor Commented:
Thanks for your inputs.  The WatchGuard tech said there was no log to proof these email came from external, in other word it didn't pass through the WatchGuard appliance.

I checked the Exchange message tracker, searched by sender, recipient email address that I saw in quarantined messages but found no results.  It is possible that Vipre may have removed these messages as suspected viruses as to why I am not finding any results.

Thank you!
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tliottaCommented:
...all came through almost at the same time...

I'd also look for (1) anything like a USB drive plugged in anywhere in your network just before that time, (2) anything like a laptop connecting to your network just before that time, (3) any connections over VPN, etc., into your network just before that time, and possibly anything similar to those. With both WatchGuard and Vipre, your network seems relatively conscious of possibilities, but you never know.

Tom
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BeerTimeAuthor Commented:
Thanks Tom, we couldn't find anyone brought their own laptops to work on this particular day.  Users are already told not to use USB devices but it is hard to find if anyone did use it, we have users with iPhone and iPad connected to the corporate email.  Do you think of is there any Bot got installed on these devices?
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BeerTimeAuthor Commented:
Thanks for everyone's help.  It is still a mystery; we couldn't find the origin of the trojan email.
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