WinNT/F4IRootkit is a kernel-mode rootkit used for copy protection on certain Sony BMG audio CDs. There are several versions of this rootkit. The rootkit hides certain Windows system resources, including files, processes, and registry settings. The rootkit can be used by attackers to hide malicious content on the computer.

What to do now

Manual removal is not recommended for this threat. Use the Microsoft Malicious Software Removal Tool, Microsoft Security Essentials, Microsoft Safety Scanner, or another up-to-date scanning and removal tool to detect and remove this threat and other unwanted software from your computer. For more information on Microsoft security products, see

Threat behavior

WinNT/F4IRootkit is a kernel-mode rootkit distributed on certain Sony BMG audio CDs. These CDs use the Extended Copy Protection (XCP) technology developed by First 4 Internet Ltd (F4i).
To install the software that is on the CD, the user must be logged on to the computer with an account that has administrator privileges. When the user first inserts the CD and accepts the license agreement, the installer creates a service called $sys$aries and creates the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\$sys$aries. The installer creates a directory named $sys$filesystem under %windir%\System32 and drops a driver named aries.sys in the $sys$filesystem directory.
WinNT/F4IRootkit hides certain Windows system resources that begin with "$sys$". This includes names of files, directories, processes, and registry settings. For example, the rootkit would hide a file with a name like $sys$myfile.exe. 
The rootkit hides Windows resources by intercepting certain Windows NT kernel-mode API calls. This includes calls to the following APIs: NtCreateFile, NtQueryDirectoryFile, NtQuerySystemInformation, NtOpenKey, and NtEnumerateKey. The rootkit scans the results returned by these API calls and removes any entry in the result that has the $sys$ prefix in the name. For example, if a user lists the contents of %windir%\System32, the rootkit examines the result returned from NtQueryDirectoryFile and removes any directory or file entry that begins with $sys$, so that the entry is not visible to the user.
Although WinNT/F4IRootkit was originally intended to help prevent CD duplication, attackers can use the rootkit in other ways. For example, when the backdoor Trojan Win32/Ryknos infects a computer, it uses WinNT/F4IRootkit to hide if the rootkit is already installed on the computer. For more information, see the encyclopedia entry for Win32/Ryknos.


There are no readily apparent indications of infection by WinNT/F4IRootkit. However, your computer is probably infected by this rootkit if the file aries.sys is in a folder named $sys$filesystem under the Windows system directory.
To check for the presence of aries.sys
  1. Click Start, and click Run.
  2. In the Open text box, type: cmd
  3. Click OK. A command-line shell appears.
  4. At the command prompt, type: dir %windir%\System32\$sys$filesystem\aries.sys
  5. Press Enter. The system displays the name aries.sys if the file is present. Otherwise, the system displays "File Not Found".


To avoid infection by WinNT/F4IRootkit, do not install software from CDs that are known to include the rootkit. Consult Sony BMG and First 4 Internet Ltd for more information.
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
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

Alert level: High
This entry was first published on: Nov 15, 2005
This entry was updated on: Apr 17, 2011

This threat is also detected as:
No known aliases