Analysis by: Roland Marco Dela Paz
ALIASES:

W32.SillyFDC (Symantec); W32/Autorun.worm.co (Mcafee)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel: Copies itself in all available physical drives, Propagates via removable drives

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

It opens a hidden Internet Explorer window.

  TECHNICAL DETAILS

File Size: 1,904,640 bytes
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 13 Jan 2011

Installation

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

  • %Program Files%\Common Files\Microsoft Shared\MSINFO\backupuser.exe
  • %Program Files%\Common Files\Microsoft Shared\MSINFO\_backupuser.exe

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

It drops the following non-malicious files:

  • %System%\drivers\oreans32.sys
  • %Program Files%\COMMON FILES\MICROSOFT SHARED\MSInfo\FieleWay.txt

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

Autostart Technique

This worm registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Windows_XP
ImagePath = %Program Files%\Common Files\Microsoft Shared\MSINFO\backupuser.exe

Other System Modifications

This worm adds the following registry entries as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\WinLicense
CheckIN = 1

Propagation

This worm drops the following copies of itself in all physical and removable drives:

  • backupuser.exe

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=backupuser.exe
shellexecute=backupuser.exe
shell\Auto\command=backupuser.exe

Backdoor Routine

This worm opens a hidden Internet Explorer window.

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 7.766.12
FIRST VSAPI PATTERN DATE: 13 Jan 2011

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_LOCAL_MACHINE\SOFTWARE
    • WinLicense
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • Windows_XP

Step 4

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.
  • %System%\drivers\oreans32.sys
  • %Program Files%\COMMON FILES\MICROSOFT SHARED\MSInfo\FieleWay.txt

Step 5

Search and delete AUTORUN.INF files created by WORM_OTORUN.WS that contain these strings

[ Learn More ]
    [AutoRun]
    open=backupuser.exe
    shellexecute=backupuser.exe
    shell\Auto\command=backupuser.exe

Step 6

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