TROJ_NSIS.BU
Trojan:Win32/Malagent (Microsoft); Generic Downloader.x (McAfee); Downloader (Symantec); ARC:NSIS (Kaspersky); Trojan.Win32.Generic!BT (Sunbelt); Trojan.Generic.3271105 (FSecure)
Windows 2000, Windows XP, Windows Server 2003
![](/vinfo/imgFiles/legend.jpg)
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 disables Task Manager, Registry Editor, and Folder Options.
TECHNICAL DETAILS
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:
- %System Root%\DOCUME~1
- %System Root%\DOCUME~1\ADMINI~1
- %User Profile%\LOCALS~1
- %User Temp%\nsz3.tmp
(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.. %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.. %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.)
Autostart Technique
This Trojan registers itself as a BHO to ensure its automatic execution every time Internet Explorer is used by adding the following registry keys:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Browser Helper Objects\{b448d946-3623-42ab-ba32-c08651e36980}
It modifies the following registry entries to ensure it automatic execution at every system startup:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "{random characters}"
(Note: The default value data of the said registry entry is Explorer.exe.)
Other System Modifications
This Trojan deletes the following files:
- %User Temp%\nst1.tmp
- %User Temp%\nsz3.tmp
(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.)
It adds the following registry keys:
HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\SystemRestore
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
HKEY_CURRENT_USER\SOFTWARE\Policies\
Microsoft\WindowsFirewall\DomainProfile
HKEY_CURRENT_USER\SOFTWARE\Policies\
Microsoft\WindowsFirewall\StandardProfile
HKEY_CURRENT_USER\Software\Policies\
Microsoft\Windows\WindowsUpdate\
AU
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\WindowsFirewall\DomainProfile
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\WindowsFirewall\StandardProfile
HKEY_CLASSES_ROOT\CLSID\{b448d946-3623-42ab-ba32-c08651e36980}
HKEY_CLASSES_ROOT\CLSID\{b448d946-3623-42ab-ba32-c08651e36980}\
InProcServer32
It adds the following registry entries:
HKEY_CURRENT_USER\Software\Microsoft\
Security Center
FirewallDisableNotify = "1"
HKEY_CURRENT_USER\Software\Microsoft\
Security Center
UpdatesDisableNotify = "1"
HKEY_CURRENT_USER\Software\Microsoft\
Security Center
AntiVirusDisableNotify = "1"
HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\CurrentVersion\SystemRestore
DisableSR = "1"
HKEY_CURRENT_USER\Software\Policies\
Microsoft\WindowsFirewall\DomainProfile
EnableFirewall = "0"
HKEY_CURRENT_USER\Software\Policies\
Microsoft\WindowsFirewall\StandardProfile
EnableFirewall = "0"
HKEY_CURRENT_USER\Software\Policies\
Microsoft\Windows\WindowsUpdate\
AU
AUOptions = "1"
HKEY_CURRENT_USER\Software\Policies\
Microsoft\Windows\WindowsUpdate\
AU
NoAutoUpdate = "1"
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\WindowsFirewall\DomainProfile
EnableFirewall = "0"
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\WindowsFirewall\StandardProfile
EnableFirewall = "0"
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\WindowsUpdate\
AU
AUOptions = "1"
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\
Microsoft\Windows\WindowsUpdate\
AU
NoAutoUpdate = "1"
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
CLSID\{b448d946-3623-42ab-ba32-c08651e36980}\InProcServer32
ThreadingModel = "Apartment"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Browser Helper Objects\{b448d946-3623-42ab-ba32-c08651e36980}
NoExplorer = "1"
It modifies the following registry entries:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Security Center
FirewallDisableNotify = "1"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Security Center
UpdatesDisableNotify = "1"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Security Center
AntiVirusDisableNotify = "1"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SystemRestore
DisableSR = "1"
It creates the following registry entry(ies) to disable Task Manager, Registry Tools and Folder Options:
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Policies\
System
DisableRegistryTools = "1"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
DisableRegistryTools = "1"
Dropping Routine
This Trojan drops the following files:
- %User Temp%\nsj2.tmp
- %User Temp%\nsz3.tmp\NSISdl.dll
- %Program Files%\Common Files\System\sys_vd4.dat
- tmp.back
- %Program Files%\Common Files\System\svchost.exe
(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.. %Program Files% is the default Program Files folder, usually C:\Program Files.)
This report is generated via an automated analysis system.
SOLUTION
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 TROJ_NSIS.BU using either the Startup Disk or Recovery Console
Step 3
Close all opened browser windows
Step 4
Enable Registry Editor, Task Manager, and Folder options
Step 5
Delete this registry key
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 NT\CurrentVersion
- SystemRestore
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies
- System
- In HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\WindowsFirewall
- DomainProfile
- In HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\WindowsFirewall
- StandardProfile
- In HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\WindowsUpdate
- AU
- In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\WindowsFirewall
- DomainProfile
- In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\WindowsFirewall
- StandardProfile
- In HKEY_CLASSES_ROOT\CLSID
- {b448d946-3623-42ab-ba32-c08651e36980}
- In HKEY_CLASSES_ROOT\CLSID\{b448d946-3623-42ab-ba32-c08651e36980}
- InProcServer32
Step 6
Delete this registry value
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\Security Center
- FirewallDisableNotify = "1"
- In HKEY_CURRENT_USER\Software\Microsoft\Security Center
- UpdatesDisableNotify = "1"
- In HKEY_CURRENT_USER\Software\Microsoft\Security Center
- AntiVirusDisableNotify = "1"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\SystemRestore
- DisableSR = "1"
- In HKEY_CURRENT_USER\Software\Policies\Microsoft\WindowsFirewall\DomainProfile
- EnableFirewall = "0"
- In HKEY_CURRENT_USER\Software\Policies\Microsoft\WindowsFirewall\StandardProfile
- EnableFirewall = "0"
- In HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\WindowsUpdate\AU
- AUOptions = "1"
- In HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\WindowsUpdate\AU
- NoAutoUpdate = "1"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\WindowsFirewall\DomainProfile
- EnableFirewall = "0"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\WindowsFirewall\StandardProfile
- EnableFirewall = "0"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU
- AUOptions = "1"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU
- NoAutoUpdate = "1"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{b448d946-3623-42ab-ba32-c08651e36980}\InProcServer32
- ThreadingModel = "Apartment"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Browser Helper Objects\{b448d946-3623-42ab-ba32-c08651e36980}
- NoExplorer = "1"
Step 7
Restore this modified registry value
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\Security Center
- FirewallDisableNotify = "1"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Security Center
- UpdatesDisableNotify = "1"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Security Center
- AntiVirusDisableNotify = "1"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SystemRestore
- DisableSR = "1"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
- From: Shell = "{random characters}"
To: Shell = ""Explorer.exe""
- From: Shell = "{random characters}"
Step 8
Search and delete these files
- %User Temp%\nsj2.tmp
- %User Temp%\nsz3.tmp\NSISdl.dll
- %Program Files%\Common Files\System\sys_vd4.dat
- tmp.back
- %Program Files%\Common Files\System\svchost.exe
Step 9
Search and delete these folders
- %System Root%\DOCUME~1
- %System Root%\DOCUME~1\ADMINI~1
- %User Profile%\LOCALS~1
- %User Temp%\nsz3.tmp
Step 10
Scan your computer with your Trend Micro product to delete files detected as TROJ_NSIS.BU. 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 11
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 Temp%\nst1.tmp
- %User Temp%\nsz3.tmp
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