Analysis by: Michael Cabel
 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Propagates via removable drives

This worm arrives via removable drives. It may be unknowingly downloaded by a user while visiting malicious websites.

It drops copies of itself in all removable drives. It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

  TECHNICAL DETAILS

File Size: 179,284 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 28 Jan 2008

Arrival Details

This worm arrives via removable drives.

It may be unknowingly downloaded by a user while visiting malicious websites.

Installation

This worm drops the following copies of itself into the affected system:

  • %System%\win.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

Autostart Technique

This worm modifies the following registry entry(ies) to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Userinit = "%System%\userinit.exe,%System%\win.exe,"

(Note: The default value data of the said registry entry is "%System%\userinit.exe,".)

Propagation

This worm drops copies of itself in all removable drives.

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[AutoRun]
Open= .\RECYCLER\{Random SID}\{Malware File Name}.exe
shell\Open\command= .\RECYCLER\{Random SID}\{Malware File Name}.exe
shell\open\Default=1
shell\explore\Command= .\RECYCLER\{Random SID}\{Malware File Name}.exe

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 4.966.08
FIRST VSAPI PATTERN DATE: 28 Jan 2008

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

Identify and delete files detected as WORM_AUTORUN.ACH using the Recovery Console

[ Learn More ]

Step 3

Restore this modified 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 NT\CurrentVersion\Winlogon
    • From: Userinit = "%System%\userinit.exe,%System%\win.exe,"
      To: "%System%\userinit.exe,"

Step 4

Search and delete AUTORUN.INF files created by WORM_AUTORUN.ACH that contain these strings

[ Learn More ]
[AutoRun]
Open= .\RECYCLER\{Random SID}\{Malware File Name}.exe
shell\Open\command= .\RECYCLER\{Random SID}\{Malware File Name}.exe
shell\open\Default=1
shell\explore\Command= .\RECYCLER\{Random SID}\{Malware File Name}.exe

Step 5

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_AUTORUN.ACH. 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.


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