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TROJ_AGENT.EWC

October 12, 2012
 ALIASES:

Trojan:Win32/Stresid.C (Microsoft); Spy-Agent.bf.dldr (McAfee); Trojan.Linkoptimizer (Symantec); Trojan.Win32.Scar.fdzf (Kaspersky); Trojan.Obfus.5.Gen (FSecure)

 PLATFORM:

Windows 2000, Windows, XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

64,512 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

26 Nov 2011

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This Trojan creates the following folders:

  • %Windows%\SoftwareDistribution
  • %Windows%\SoftwareDistribution\DataStore\Logs\
  • %Windows%\SoftwareDistribution\DataStore

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
yfop1.exe = "%Temp%\yfop1.exe"

Other System Modifications

This Trojan deletes the following files:

  • %Temp%\1.tmp
  • %Windows%\SoftwareDistribution\DataStore\Logs\edbtmp.log

(Note: %Temp% is the Windows Temporary folder, which is usually C:\Windows\Temp or C:\WINNT\Temp.. %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

It adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
RASModule

HKEY_CURRENT_USER\Software\Microsoft\
RASModule\Data

HKEY_LOCAL_MACHINE\Software\Microsoft\
RFC1156Agent\CurrentVersion\Parameters

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows
Last = 6c9aa49e

HKEY_CURRENT_USER\Software\Microsoft\
Windows
Last = 6c9aa49e

HKEY_CURRENT_USER\Software\Microsoft\
RASModule\Data
Limit = {random values}

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\ZEC
ImagePath = ""%Program Files%\Common Files\System\Kzs.exe""

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
RFC1156Agent\CurrentVersion\Parameters
TrapPollTimeMilliSecs = 3a98

Dropping Routine

This Trojan drops the following files:

  • %Program Files%\Common Files\System\Kzs.exe

(Note: %Program Files% is the default Program Files folder, usually C:\Program Files.)

Other Details

This Trojan deletes the initially executed copy of itself

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine:

9.200

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

Delete this registry key

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft
    • RASModule
  • In HKEY_CURRENT_USER\Software\Microsoft\RASModule
    • Data
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\RFC1156Agent\CurrentVersion
    • Parameters

Step 4

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • yfop1.exe="%Temp%\yfop1.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows
    • Last=6c9aa49e
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows
    • Last=6c9aa49e
  • In HKEY_CURRENT_USER\Software\Microsoft\RASModule\Data
    • Limit={random values}
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\ZEC
    • ImagePath=""%Program Files%\Common Files\System\Kzs.exe""
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\RFC1156Agent\CurrentVersion\Parameters
    • TrapPollTimeMilliSecs=3a98

Step 5

Search and delete these folders

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Windows%\SoftwareDistribution
  • %Windows%\SoftwareDistribution\DataStore\Logs\
  • %Windows%\SoftwareDistribution\DataStore

Step 6

Search and delete this file

[ Learn More ]
There may be some component files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files and folders in the search result. %Program Files%\Common Files\System\Kzs.exe

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_AGENT.EWC. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.

Step 8

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %Temp%\1.tmp
  • %Windows%\SoftwareDistribution\DataStore\Logs\edbtmp.log


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