Win32/Nuwar refers to a family of Trojan droppers that install a distributed peer-to-peer (P2P) downloader Trojan. This downloader Trojan in turn downloads a copy of the email worm component of Win32/Nuwar.

What to do now

To detect and remove this threat and other malicious software that may be installed in your computer, run a full-system scan with an up-to-date antivirus product such as the following:
For more information on antivirus software, see

Threat behavior

Win32/Nuwar refers to a family of Trojan droppers that install a distributed peer-to-peer (P2P) downloader Trojan. This downloader Trojan in turn downloads a copy of the email worm component of Win32/Nuwar.
The email worm component does the following:
  • Drops a file with a random name into the directory in which it is executed.
  • This file creates a driver in the Windows system folder (by default, on Windows XP and Vista, this folder is C:\Windows\System32. The dropped file is usually named wincom32.sys.
  • This driver contains the main payload functionality of the worm, and is used to inject an embedded dll into running processes which enlists the computer in a private peer-to-peer (p2p) network.
  • The injected dll drops an initialization file, typically named wincom32.ini, in the Windows system folder which contains its network peer information. This file is detected as Worm:Win32/Nuwar!ini.
  • The driver is added as a service to run whenever Windows starts. The service is typically named 'wincom32'
  • On Windows XP or earlier, the driver will stealth references to this driver so that the driver and its service cannot be seen.
Email Characteristics
To obtain addresses in order to spread, Win32/Nuwar enumerates the first 30000 files under 122k on all fixed and remote drives. The worm does not use domains containing 'microsoft' or domains ending in .gov or .mil. The worm performs DNS queries on the email address domains to check their legitimacy. The worm will spoof the sender address to be a randomly chosen name from a list from the domain. The message body will be blank. The subject line of the email generally uses fictitious and incendiary topics, for example:
  • USA Declares War on Iran
  • 230 dead as storm batters Europe
  • USA Missle Strike: Iran War just have started
  • Naked teens attack home director
The email includes an executable (.EXE) attachment which may use on of the following file names:
  • More.exe
  • Read More.exe
  • Click Here.exe
  • Click Me.exe
  • Read Me.exe
  • Movie.exe
  • News.exe
  • Video.exe
Win32/Nuwar attempts to stop processes with process or window names containing substrings typically related to various security-related software products.
Some variants of Win32/Nuwar may be referred to as the Storm worm.
Related Malware


Win32/Nuwar uses advanced stealth techniques in order to hide its files and associated registry modifications. Hence, it is unlikely that users could easily ascertain the presence of the Trojan on the infected computer.


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 web pages.
  • 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.
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.
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
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:
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 web pages
Exercise caution with links to web pages 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

Alert level: High
This entry was first published on: Sep 07, 2007
This entry was updated on: Apr 17, 2011

This threat is also detected as:
  • Win32/Pecoan (CA)
  • W32/Nuwar@MM (McAfee)
  • Storm Worm (other)