Analysis by: Marfel Tiamzon
ALIASES:

Microsoft: Virus:Win32/Virut.BN; Mcafee: W32/Virut.n.gen

 PLATFORM:

Windows 2000, XP, Server 2003

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

  • Threat Type: File infector

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This file infector executes the dropped file(s). As a result, malicious routines of the dropped files are exhibited on the affected system.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: Varies
File Type: PE
Memory Resident: Yes
Initial Samples Received Date: 14 Sep 2010

Installation

This file infector drops the following files:

  • %System%\drivers\sysdrv32.sys - detected as HKTL_TCPAGENT

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

It drops the following copies of itself into the affected system:

  • %WINDOWS%\system\svhost.exe

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
WSVCHO = %WINDOWS%\system\svhost.exe

Other System Modifications

This file infector adds the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\SafeBoot\Minimal\
SVCWINSPOOL

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\SafeBoot\Network\
SVCWINSPOOL

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Safeboot\Minimal\
SVCWINSPOOL
@ = Service

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Safeboot\Network\
SVCWINSPOOL
@ = Service

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
%WINDOWS%\system\svhost.exe = %WINDOWS%\system\svhost.exe:*:Enabled:svhost

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile\AuthorizedApplications\
List
\??\%system%\winlogon.exe = \??\%system%\winlogon.exe:*:enabled:@shell32.dll,-1

File Infection

This file infector infects the following file types:

  • EXE
  • SCR

It avoids infecting files that contain the following strings in their names:

  • WINC
  • WCUN
  • WC32
  • OTSP

Dropping Routine

This file infector executes the dropped file(s). As a result, malicious routines of the dropped files are exhibited on the affected system.

Other Details

This file infector deletes itself after execution.

  SOLUTION

Minimum Scan Engine: 8.900

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

Remove the malware/grayware file dropped/downloaded by PE_VIRUX.KR

     
    • HKTL_TCPAGENT

Step 3

Restart in Safe Mode

[ Learn More ]

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 KEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • %WINDOWS%\system\svhost.exe = %WINDOWS%\system\svhost.exe:*:Enabled:svhost
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile\AuthorizedApplications\List
    • \??\%system%\winlogon.exe = \??\%system%\winlogon.exe:*:enabled:@shell32.dll,-1

Step 5

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot\Minimal\
    • SVCWINSPOOL
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot\Network\
    • SVCWINSPOOL

Step 6

Scan your computer with your Trend Micro product to clean files detected as PE_VIRUX.KR. 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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