Win32/Nuwar.gen threat description - Microsoft Security Intelligence

Threat behavior

Win32/Nuwar.gen is generic detection for 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.gen. 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.gen 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 yahoo.com 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.gen attempts to stop processes with process or window names containing substrings typically related to various security-related software products.

Prevention

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 Web sites.

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 http://www.microsoft.com/security/antivirus/av.aspx.

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 e-mail 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 Web page 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 Web page 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 8 characters, and combines letters, numbers, and symbols. For more information, see http://www.microsoft.com/protect/yourself/password/create.mspx.

Win32/Nuwar.gen

Summary

What to do now

Technical information