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False Positive sm56co85.txt (Extension.Mismatch)


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I updated my database to version 4257 today (29-June-2010) and a subsequent quick scan with MBAM detected an infected file at C:\Windows\System32\sm56co85.txt (Extension.Mismatch). I'm not certain, but just based on the name of the file, I believe this is a valid file installed as part of my Motorola SM56 speakerphone modem software (v. I haven't updated my modem software since 24-Nov-2009 so this file has likely been on my laptop for several months and was just recently detected as a false positive by a recent MBAM database version.

A quick scan run yesterday (28-June-2010) with database version 4233 did not detect this file as infected. I own a registered version of MBAM but do not have MBAM realtime protection enabled because I already have Norton Internet Security 2010 running on my laptop.

After I quarantined C:\Windows\System32\sm56co85.txt, I ran a full scan of my hard drives with MBAM (database version 4257) and there were no other infections on my laptop. My dial-up connection still works so it doesn't appear that removing this file caused any harm.

The scan log (run in developer's mode) is posted below. A .rar file containing the suspicious sm56co85.txt file is attached.


Malwarebytes' Anti-Malware 1.46


Database version: 4257

Windows 6.0.6002 Service Pack 2

Internet Explorer 8.0.6001.18928

29/06/2010 7:27:07 PM

mbam-log-2010-06-29 (19-27-07).txt

Scan type: Quick scan

Objects scanned: 136687

Time elapsed: 3 minute(s), 20 second(s)

Memory Processes Infected: 0

Memory Modules Infected: 0

Registry Keys Infected: 0

Registry Values Infected: 0

Registry Data Items Infected: 0

Folders Infected: 0

Files Infected: 1

Memory Processes Infected:

(No malicious items detected)

Memory Modules Infected:

(No malicious items detected)

Registry Keys Infected:

(No malicious items detected)

Registry Values Infected:

(No malicious items detected)

Registry Data Items Infected:

(No malicious items detected)

Folders Infected:

(No malicious items detected)

Files Infected:

C:\Windows\System32\sm56co85.txt (Extension.Mismatch) -> No action taken. [DD659E4D49829416087834C2A4C4B213]


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  • 1 month later...

Just following up to my original post. Has anyone from Malwarebytes' investigated if the sm56co85.txt file I submitted is a legitimate threat?

I searched the Symantec and McAfee sites and couldn't find sm56co85.txt listed as a known threat. When I googled "sm56co85.txt", the three sites listed below indicate that sm56co85.txt may be a legitimate file that is required of the Motorola SM56 modem software, but the majority of sites indicated that this file can also contain dangerous code that could hijack your system.




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  • Staff

The reason MBAM detects this file as extension mismatch is it's an executable file (exe or dll) but with a .txt extension. This file is ok and can be safely added to your ignore list. Unfortunately this is very a very poor practice on the part of Motorola as most malware does this in an effort to try to hide their files. This is most likely a leftover temporary file from the install.

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I have the following four sm56*.* files in my C:\Windows\System32\DriverStore\FileRepository\smserial.inf_e085855c\x86\ folder:

- sm56.dll (192KB, version, created 04-Apr-2007, Motorola Inc., Common specific Vista functions for SM56 Helper)

- sm56.reg (309 KB, version unknown, created 12-Mar-2009, Registration Entries)

- sm56co85.dll (504 KB, version, created 26-Oct-2009, Motorola Inc., SM56 Modem co-installer)

- sm56hlpr.exe (1.39 MB, version, created 26-Oct-2009, Motorola Inc., SM56 Modem Helper

I followed your suggestion and temporarily renamed the suspect sm56co85.txt file in the C:\Windows\System32\ folder to sm56co85.txt.exe. I was then able to view the complete file properties (504 KB, version, created 26-Oct-2009, Motorola Inc., SM56 Modem co-installer), which confirms your theory that this sm56co85.txt file is likely a copy of my sm56co85.dll library.

I checked my Windows Update history, and my last Motorola SM56 Modem update (version was delivered on 24-Nov-2009. This update failed the first time I attempted the installation (I received 4 other large Windows updates that same day and suspect that I was prompted to re-start my machine before the modem software installation was complete) so it's possible that the sm56co85.txt file was left behind when some old/temp files were not cleaned up properly.

Thanks for your help.

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