Symantec Security Response - Trojan.Qhosts © 1995-2003 Symantec Corporation. All rights reserved. Legal Notices Privacy Policy Trojan.Qhosts Discovered on: October 01, 2003 Last Updated on: October 02, 2003 10:08:13 AM Trojan.Qhosts is a Trojan Horse that will modify the TCP/IP settings to point to a different DNS server. Trojan.Qhosts cannot spread by itself. For a computer to become infected, you would have to open an HTML page that contains code, which allows it to open a viral HTML file on the target computer, so that the script can create and run the malicious executable. Also Known As: QHosts-1 [McAfee], VBS.QHOSTS [CA] Type: Trojan Horse Infection Length: 4,096 bytes(BAT file), 76KB(HTML file), 41 KB(EXE file) Systems Affected: Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows Server 2003, Windows XP Systems Not Affected: DOS, Linux, Macintosh, OS/2, UNIX, Windows 3.x Virus Definitions (Intelligent Updater) * October 02, 2003 Virus Definitions (LiveUpdate™) ** October 08, 2003 *Intelligent Updater definitions are released daily, but require manual download and installation. Click here to download manually. **LiveUpdate virus definitions are usually released every Wednesday. Click here for instructions on using LiveUpdate. Wild: Number of infections: 0 - 49 Number of sites: 0 - 2 Geographical distribution: Low Threat containment: Easy Removal: Easy Threat Metrics Wild: LowDamage: LowDistribution: Low When the Trojan.Qhosts HTML file is opened, it performs the following actions: Creates the file, %System%\Aolfix.exe. Executes the Aolfix.exe file, which then performs the following actions: Creates the hidden folder C:\Bdtmp\Tmp. Creates and runs the batch file C:\Bdtmp\Tmp\.bat. Deletes the C:\Bdtmp\Tmp\.bat file. Batch file When the C:\Bdtmp\Tmp\.bat file is executed, it does the following: Creates the files: %Windir%\o.reg %Windir%\o2.reg %Windir%\o.vbs Note: %Windir% is a variable. The batch file locates the Windows installation folder (by default, this is C:\Windows or C:\Winnt) and copies itself to that location. Runs the .reg files, which does the following: Adds the values: "EnableDNS"="1" "NameServer"="" "HostName"="host" "Domain"="mydomain.com" to the registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VxD\MSTCP so that the DNS server, which the computer uses, will be the one that the Trojan's creator specified. Adds the values: "ProxyEnable"="0" "MigrateProxy"="0" to the registry key: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings Adds the values: "Use Search Asst"="no" "Search Page"="http://www.google.com" "Search Bar"="http://www.google.com/ie" to the registry key: HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main Adds the value: ""="http://www.google.com/keyword/%%s" "provider"="gogl" to the registry key: HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\SearchURL Adds the value: "SearchAssistant"="http://www.google.com/ie" to the registry key: HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Search Adds the value: "r0x"="your s0x" to the registry keys: HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Tcpip\Parameters\interfaces\windows HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Tcpip\Parameters\interfaces\windows Modifies the Hosts file to point many different URLs to the IP, which the Trojan's creator specifies. Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices": Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates. If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied. Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services. Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised. Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files. Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media. Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched. The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines. Disable System Restore (Windows Me/XP). Update the virus definitions. Run a full system scan and delete all the files detected as Trojan.Qhosts. Reverse the changes that were made to the registry. Reverse the changes that were made to the Hosts file. For specific details on each of these steps, read the following instructions. Note: Steps 4 and 5 are somewhat complex and are only necessary if the Trojan has actually executed. 1. Disabling System Restore (Windows Me/XP) If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer. Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations. Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat. For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles: "How to disable or enable Windows Me System Restore" "How to turn off or turn on Windows XP System Restore" Note: When you are completely finished with the removal procedure, and you are satisfied that the threat has been removed, you should reenable System Restore by following the instructions in the aforementioned documents. For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455. 2. Updating the virus definitions Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. Currently, only the Intelligent Updaters contain detection for this threat. Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater). The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions. 3. Scanning for and deleting the infected files Start your Symantec antivirus program and make sure that it is configured to scan all the files. For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files." For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec Corporate antivirus product is set to scan all files." Run a full system scan. If any files are detected as infected with Trojan.Qhosts, click Delete. 4. Reversing the changes made to the registry WARNING: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry," for instructions. Click Start, and then click Run. (The Run dialog box appears.) Type regedit Then click OK. (The Registry Editor opens.) Navigate to the key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VxD\MSTCP In the right pane, delete the values: "EnableDNS"="1" "NameServer"="" "HostName"="host" "Domain"="mydomain.com" Navigate to the key: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings In the right pane, delete the values: "ProxyEnable"="0" "MigrateProxy"="0" Navigate to the key: HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main In the right pane, delete the values: "Use Search Asst"="no" "Search Page"="http://www.google.com" "Search Bar"="http://www.google.com/ie" Navigate to the key: HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\SearchURL In the right pane, delete the values: ""="http://www.google.com/keyword/%%s" "provider"="gogl" Navigate to the key: HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Search In the right pane, delete the value: "SearchAssistant"="http://www.google.com/ie" Navigate to the keys: HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Tcpip\Parameters\interfaces\windows HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Tcpip\Parameters\interfaces\windows In the right pane, delete the value: "r0x"="your s0x" Exit the registry Editor. 5. Reversing the changes made to the Hosts file All the computers will not have this file, and the location can vary. For example, if the file exists in Windows 98, it will usually be in C:\Windows; and in Windows 2000, it is in the C:\WINNT\SYSTEM32\DRIVERS\ETC folder. Also, there may be multiple copies of this file in different locations. The most efficient way to locate the file is to search for it. Follow the instructions for your operating system: Windows 95/98/Me/NT/2000 Click Start, point to Find or Search, and then click Files or Folders. Make sure that "Look in" is set to (C:) and that "Include subfolders" is checked. In the "Named" or "Search for..." box, type: hosts Click Find Now or Search Now. For each one that you find, right-click it, and then click "Open With." Deselect the "Always use this program to open this program" check box. Scroll through the list of programs and double-click Notepad. Look for the following lines and delete them, if found: elite www.google.akadns.net www.google.com google.com www.altavista.com altavista.com search.yahoo.com uk.search.yahoo.com ca.search.yahoo.com jp.search.yahoo.com au.search.yahoo.com de.search.yahoo.com search.yahoo.co.jp www.lycos.de www.lycos.ca www.lycos.jp www.lycos.co.jp alltheweb.com web.ask.com ask.com www.ask.com www.teoma.com search.aol.com www.looksmart.com auto.search.msn.com search.msn.com ca.search.msn.com fr.ca.search.msn.com search.fr.msn.be search.fr.msn.ch Close Notepad and save your changes when prompted. Windows XP Click Start, and then click Search. Click All files and folders. In the "All or part of the file name" box, type: hosts Verify that "Look in" is set to "Local Hard Drives" or to (C:). Click "More advanced options." Check "Search system folders." Check "Search subfolders." Click Search. Click Find Now or Search Now. For each one that you find, right-click it, and then click "Open With." Deselect the "Always use this program to open this program" check box. Scroll through the list of programs and double-click Notepad. Look for the following lines and delete them, if found: elite www.google.akadns.net www.google.com google.com www.altavista.com altavista.com search.yahoo.com uk.search.yahoo.com ca.search.yahoo.com jp.search.yahoo.com au.search.yahoo.com de.search.yahoo.com search.yahoo.co.jp www.lycos.de www.lycos.ca www.lycos.jp www.lycos.co.jp alltheweb.com web.ask.com ask.com www.ask.com www.teoma.com search.aol.com www.looksmart.com auto.search.msn.com search.msn.com ca.search.msn.com fr.ca.search.msn.com search.fr.msn.be search.fr.msn.ch Close Notepad and save your changes when prompted. Write-up by: Douglas Knowles