Threat behavior
Spammer:Win32/Nuwar.A!sys is a kernel-mode driver, and component of the Win32/Nuwar Trojan family, and is used to protect itself from removal, and to disable common firewalls. Spammer:Win32/Nuwar.A!sys is commonly installed as <system folder>\spooldr.sys.
The kernel-mode driver attempts to prevent any executable image with the following substrings from executing:
<system folder>\vsdatant.sys
<system folder>\drivers\bcfilter.sys
<system folder>\drivers\bcftdi.sys
<system folder>\drivers\bc_hassh_f.sys
<system folder>\drivers\bc_ip_f.sys
<system folder>\drivers\bc_ngn.sys
<system folder>\drivers\bc_pat_f.sys
<system folder>\drivers\bc_prt_f.sys
<system folder>\drivers\bc_tdi_f.sys
%ProgramFiles%\zone labs\zonealarm\zclient.exe
%ProgramFiles%\agnitum\outpost firewall\kernel\filtnt.sys
%ProgramFiles%\agnitum\outpost firewall\kernel\sandbox.sys
%ProgramFiles%\mcafee.com\personal firewall\data\drv\mpfirewall.sys
The kernel-mode driver terminates the following processes:
zlclient.exe
outpost.exe
The kernel-mode driver hides files and folders beginning with "spooldr" by hooking the ZwQueryDirectoryFile API, as well as denying access to tcpip.sys, by hooking ZwCreateFile.
Related Malware
Prevention
Take the following steps to help prevent infection on your system:
Enable a firewall on your computer.
Get the latest computer updates.
Use up-to-date antivirus software.
Use caution with attachments and file transfers.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows XP Internet Connection Firewall.
To turn on the Internet Connection Firewall in Windows XP
Click Start, and click Control Panel.
Click Network and Internet Connections. If you do not see Network and Internet Connections, click Switch to Category View.
Click Change Windows Firewall Settings.
Select On.
Click OK.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. You can use the Automatic Updates feature in Windows XP to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
To turn on Automatic Updates in Windows XP
Click Start, and click Control Panel.
Click System.
Click Automatic Updates.
Select a setting. Microsoft recommends selecting Automatic. If you do not choose Automatic, but you choose to be notified when updates are ready, a notification balloon appears when new downloads are available to install. Click the notification balloon to review and install the updates.
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 that is updated with the latest signature files. Antivirus software is available from several sources. For more information, see http://www.microsoft.com/athome/security/downloads/default.mspx
Use caution with attachments and 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.
