Win32/Nuqel is the detection for a worm family, written in AutoItScript, that spreads by copying themselves to writeable network shares, removable drives and via instant messaging client messages. They may also terminate certain programs and download arbitrary files from a remote server.

System changes

The following system changes may indicate the presence of this malware:

• The presence of the following registry modifications:
  
  In subkey: HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
  Sets value: "Shell"
  To data: "explorer.exe <Win32/Nuqel worm copy>"
  
  In subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run
  Sets value: "Yahoo Messengger"
  To data: "<Win32/Nuqel worm copy>"
• An inability to open a command prompt, or run Windows Task Manager and Registry Editor.

Win32/Nuqel is the detection for a worm family, written in AutoItScript, that spreads by copying themselves to writeable network shares, removable drives and via instant messaging client messages. They may also terminate certain programs and download arbitrary files from a remote server.

Installation

When run, Win32/Nuqel copies itself to one of the following folders with read-only, hidden and system attributes:

• %SystemRoot%
• %SystemRoot%\System32
• %AppData%

The worm file names are variable and could be names such as "scvhost.exe", "rvhost.exe", "regsvr.exe", "winhelp.exe" and so on. Win32/Nuqel modifies the registry to execute the worm copy at each Windows start.

In subkey: HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Sets value: "Shell"
To data: "explorer.exe <Win32/Nuqel worm copy>"

In subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run
Sets value: "Yahoo Messengger"
To data: "<Win32/Nuqel worm copy>"

Win32/Nuqel adds a scheduled task to run the worm every day at 09:00 by executing the following command.

cmd.exe /C AT 09:00 /interactive /EVERY:m,t,w,th,f,s,su <Win32/Nuqel worm copy>

To maximize the length of the time the worm will remain active, the worm modifies registry data removing time limits on AT tasks.

In subkey: HKLM\SYSTEM\CurrentControlSet\Services\Schedule
Sets value: "AtTaskMaxHours"
To data: "0"

Spreads via...

Chat client Yahoo! Messenger
Win32/Nuqel attempts to send a URL pointing to the malware hosted at a remote server location, and a message sourced from setting.ini (see the Payload section "Downloads data" below) using Yahoo! Messenger. If the worm fails to read from the configuration file, it sends messages containing one of the following texts and a URL pointing to a copy of the worm hosted at a remote server location:

• E may, vao day coi co con nho nay ngon lam
• Vao day nghe bai nay di ban
• Biet tin gi chua, vao day coi di
• Trang Web nay coi cung hay, vao coi thu di
• Toi di lang thang lan trong bong toi buot gia, ve dau khi da mat em roi? Ve dau khi bao nhieu mo mong gio da vo tan... Ve dau toi biet di ve dau?
• Khoc cho nho thuong voi trong long, khoc cho noi sau nhe nhu khong. Bao nhieu yeu thuong nhung ngay qua da tan theo khoi may bay that xa...
• Tha nguoi dung noi se yeu minh toi mai thoi thi gio day toi se vui hon. Gio nguoi lac loi buoc chan ve noi xa xoi, cay dang chi rieng minh toi...
• Loi em noi cho tinh chung ta, nhu doan cuoi trong cuon phim buon. Nguoi da den nhu la giac mo roi ra di cho anh bat ngo...
• Tra lai em niem vui khi duoc gan ben em, tra lai em loi yeu thuong em dem, tra lai em niem tin thang nam qua ta dap xay. Gio day chi la nhung ky niem buon...

Win32/Nuqel spreads itself by copying <copied file> as "New Folder.exe" and dropping autorun.ini (read only, hidden, system attributes) to the network share folder read from HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\WorkgroupCrawler\Shares. It also copies %systemroot%\<Win32/Nuqel worm copy> as <folder name>.exe to all folders (includes sub) of the network share, <folder name> here refers to all the directory name in the network share and its sub folders. After these actions, it writes one of those copied file paths to registry key HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\WorkgroupCrawler\Shares.

Win32/Nuqel spreads itself by copying <copied file> as "New Folder.exe" and dropping autorun.ini (read only, hidden, system attribute) to all removable drives. It also copies <copied file> as <folder name>.exe to all folders (includes sub) of the removable drives, <folder name> here refers to all the folder name in the removable drive and its sub folders.

Payload

Disables Windows utilities
Win32/Nuqel modifies registry data to disable Windows Task Manager and Registry Editor.

Take the following steps to help prevent infection on your computer:

• Enable a firewall on your computer.
• Get the latest computer updates for all your installed software.
• Use up-to-date antivirus software.
• Limit user privileges on the computer.
• Use caution when opening attachments and accepting file transfers.
• Use caution when clicking on links to webpages.
• Avoid downloading pirated software.
• Protect yourself against social engineering attacks.
• Use strong passwords.

Enable a firewall on your computer

Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.

• How to turn on the Windows Firewall in Windows 7
• How to turn on the Windows Firewall in Windows Vista
• How to turn on the Windows firewall in Windows XP

Get the latest computer updates

Updates help protect your computer from viruses, worms, and other threats as they are discovered. It is important to install updates for all the software that is installed in your computer. These are usually available from vendor websites.

You can use the Automatic Updates feature in Windows to automatically download future Microsoft security updates while your computer is on and connected to the Internet.

• How to turn on Automatic Updates in Windows 7
• How to turn on Automatic Updates in Windows Vista
• How to turn on Automatic Updates in Windows XP

Use up-to-date antivirus software

Most antivirus software can detect and prevent infection by known malicious software. To help protect you from infection, you should always run antivirus software, such as Microsoft Security Essentials, that is updated with the latest signature files. For more information, see http://www.microsoft.com/windows/antivirus-partners/.

Limit user privileges on the computer

Starting with Windows Vista and Windows 7, Microsoft introduced User Account Control (UAC), which, when enabled, allowed users to run with least user privileges. This scenario limits the possibility of attacks by malware and other threats that require administrative privileges to run.

You can configure UAC in your computer to meet your preferences:

• User Account Control in Windows 7
• User Account Control in Windows Vista
• Applying the Principle of Least Privilege in Windows XP
• More on User Account Control

Use caution when opening attachments and accepting file transfers

Exercise caution with email and attachments received from unknown sources, or received unexpectedly from known sources. Use extreme caution when accepting file transfers from known or unknown sources.

Use caution when clicking on links to webpages

Exercise caution with links to webpages that you receive from unknown sources, especially if the links are to a webpage that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your computer simply by visiting a webpage with harmful content.

Avoid downloading pirated software

Threats may also be bundled with software and files that are available for download on various torrent sites. Downloading "cracked" or "pirated" software from these sites carries not only the risk of being infected with malware, but is also illegal. For more information, see 'The risks of obtaining and using pirated software'.

Protect yourself from social engineering attacks

While attackers may attempt to exploit vulnerabilities in hardware or software to compromise a computer, they also attempt to exploit vulnerabilities in human behavior to do the same. When an attacker attempts to take advantage of human behavior to persuade the affected user to perform an action of the attacker's choice, it is known as 'social engineering'. Essentially, social engineering is an attack against the human interface of the targeted computer. For more information, see 'What is social engineering?'.

Use strong passwords

Attackers may try to gain access to your Windows account by guessing your password. It is therefore important that you use a strong password – one that cannot be easily guessed by an attacker. A strong password is one that has at least eight characters, and combines letters, numbers, and symbols. For more information, see http://www.microsoft.com/protect/yourself/password/create.mspx.

To detect and remove this threat and other malicious software that may be installed on your computer, run a full-system scan with an appropriate, up-to-date, security solution. The following Microsoft products detect and remove this threat:

• Microsoft Security Essentials
• Microsoft Safety Scanner
• Microsoft Windows Malicious Software Removal Tool

For more information on antivirus software, see http://www.microsoft.com/windows/antivirus-partners/.

Recovering from recurring infections on a network

The following additional steps may need to be taken to completely remove this threat from an infected network, and to stop infections from recurring from this and other similar types of network-spreading malware:

1. Ensure that an antivirus product is installed on ALL computers connected to the network that can access or host shares.
2. Ensure that all available network shares are scanned with an up-to-date antivirus product.
3. Restrict permissions as appropriate for network shares on your network. For more information on simple access control, please see: http://technet.microsoft.com/library/bb456977.aspx.
4. Remove any unnecessary network shares or mapped drives.

Note: Additionally it may be necessary to temporarily change the permission on network shares to read-only until the disinfection process is complete.

Enabling registry editor

This threat may modify the computer to prevent Registry Editor from running. To enable Registry Editor in your computer, please do the following:

1. Run a command prompt. Click Start>Run and type cmd.
2. In the command prompt, type the following as is and press Enter:
   reg.exe add HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System /v DisableRegistryTools /t REG_DWORD /d 0 /f
3. Type exit at the command prompt.

Additional remediation instructions

This threat may make lasting changes to a computer's configuration that are NOT restored by detecting and removing this threat. For more information on returning an infected computer to its pre-infected state, please see the following article/s:

Restoring the system registry

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, refer to the following articles:

• 256986 Description of the Microsoft Windows Registry
• 322756 How to back up and restore the registry in Windows

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

To remove/modify the changes that this malware has made to your computer, follow these steps:

1. Click Start and then click Run.
2. In the Open box, type regedit and then click OK.
3. Locate and then click on the following registry key:
   HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
4. On the right panel, right-click on the following registry entry:
   Shell
5. Select Modify and then click OK.
6. In the "Value data:" entry box, edit the data such that it only contains the following:
   explorer.exe
7. Close Registry Editor.