TROJ_SMALL.MZL

July 09, 2013
 ALIASES:

TrojanDownloader:Win32/Small (Microsoft); Generic Downloader.x!gjp (McAfee); Trojan Horse (Symantec); Trojan-Downloader.Win32.Injecter.kvz, Trojan-Downloader.Win32.Injecter.kvz (Kaspersky); Trojan.Win32.Generic.pak!cobra (Sunbelt); Trojan.Generic.KD.601111 (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.

  TECHNICAL DETAILS

File Size:

192,512 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

09 Jul 2012

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 drops the following copies of itself into the affected system:

  • %User Profile%\Application Data\explorer64.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Windows Explorer 64-Bit = "%User Profile%\Application Data\explorer64.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
Windows Explorer 64-Bit = "%User Profile%\Application Data\explorer64.exe"

Other System Modifications

This Trojan deletes the following files:

  • %User Profile%\Application Data\explorer64.exe
  • %Temp%\scs1.tmp
  • %Temp%\scs2.tmp

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.. %Temp% is the Windows Temporary folder, which is usually C:\Windows\Temp.)

Dropping Routine

This Trojan drops the following files:

  • %User Profile%\Application Data\svchost64.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}e.com/dl/152684338/27c0aac/b.jpg.html

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine:

9.200

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • Windows Explorer 64-Bit = "%User Profile%\Application Data\explorer64.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • Windows Explorer 64-Bit = "%User Profile%\Application Data\explorer64.exe"

Step 4

Search and delete this file

[ Learn More ]
There may be some 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.
  • %User Profile%\Application Data\svchost64.exe

Step 5

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_SMALL.MZL. 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 6

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.

  • %User Profile%\Application Data\explorer64.exe
  • %Temp%\scs1.tmp
  • %Temp%\scs2.tmp


Did this description help? Tell us how we did.