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 (for example, all Windows-based computers should
have the current Service Pack installed.). Additionally, please apply any
security updates that are mentioned in this writeup, in trusted Security
Bulletins, or on vendor Web sites.
- 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.
- Delete any values added to the registry.
- Edit the Win.ini file.
- Edit the System.ini file.
- Clear the Temporary Internet Files folder.
For specific details on each of these steps, read the following instructions.
1. To disable 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:
Note: When you are completely finished with the removal procedure and are
satisfied that the threat has been removed, 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. To update the virus definitions
Symantec Security Response fully tests all the virus definitions for quality
assurance before they are posted to our servers. There are two ways to obtain
the most recent virus definitions:
- Running LiveUpdate, which is the easiest way to obtain virus definitions:
These virus definitions are posted to the LiveUpdate servers once each week
(usually on Wednesdays), unless there is a major virus outbreak. To
determine whether definitions for this threat are available by LiveUpdate,
refer to Virus
Definitions (LiveUpdate).
- Downloading the definitions using the Intelligent Updater: The Intelligent
Updater virus definitions are posted daily. 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 Virus
Definitions (Intelligent Updater).
The latest Intelligent Updater virus definitions can be obtained here: Intelligent
Updater virus definitions. For
detailed instructions read the document: How
to update virus definition files using the Intelligent Updater.
3. To scan for and delete the infected files
- Start your Symantec antivirus program and make sure that it is configured
to scan all the files.
- Run a full system scan.
- If any files are detected, take note of the file names, and click Delete.
If the infected files are detected in the \Temporary Internet
Files\Content.IE5, due to the design of the operating system, you will not
be able to delete them. Write down the entire path and file name and clear
the Temporary Internet Files Folder at the end of the removal instructions.
Important: If you are unable to start your
Symantec antivirus product or the product reports that it cannot delete a
detected file, you may need to stop the risk from running in order to remove it.
To do this, run the scan in Safe mode. For instructions, read the document, How
to start the computer in Safe Mode. Once you have restarted in Safe
mode, run the scan again.
After the files are deleted, restart the computer in Normal mode and proceed
with the next section.
Warning messages may be displayed when the computer is restarted, since the
threat may not be fully removed at this point. You can ignore these messages and
click OK. These messages will not appear when the computer is restarted after
the removal instructions have been fully completed. The messages displayed may
be similar to the following:
Title: [FILE PATH]
Message body: Windows cannot find [FILE NAME]. Make sure you typed
the name correctly, and then try again. To search for a file, click the Start
button, and then click Search.
4. To delete the value from the registry
Important: 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 subkeys only. For instructions refer to
the document: How
to make a backup of the Windows registry.
- Click Start > Run.
- Type regedit
- Click OK.
Note: If the registry editor fails to open the threat may have
modified the registry to prevent access to the registry editor. Security
Response has developed a tool
to resolve this problem. Download and run this tool,
and then continue with the removal.
- Navigate to the subkeys:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunServices
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunServicesOnce
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\Run
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrenVersion\RunServicesOnce
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnceEx
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Explorer\Run
- In the right pane, delete any value that refers to a file that was
detected during the scan.
- Exit the Registry Editor.
5. To edit the Win.ini file
WARNING: The
following steps instruct you to remove the text from the run= line
of the Win.ini file. If you are using older programs, they may load at startup
from one of these lines. If you are sure that the text contained in these lines
is for the programs that you normally use, then we suggest that you do not
remove it.
If you are running Windows 95/98/Me, follow these steps:
- Click Start > Run.
- Type the following:
edit c:\windows\win.ini
and then click OK.
(The MS-DOS Editor opens.)
NOTE: If Windows is installed in a different location, make the
appropriate path substitution.
- In the [windows] section of the file, look for a line similar to:
run=[TROJAN FILE NAME]
Note: [TROJAN FILE NAME] refers to the file name detected during the
scan.
- If this line exists, delete everything to the right of run=
- Click File > Save.
- Click File > Exit.
6. To edit the System.ini file
If you are running Windows 95/98/Me, follow these steps:
- Click Start > Run.
- Type the following:
edit c:\windows\system.ini
and then click OK.
(The MS-DOS Editor opens.)
NOTE: If Windows is installed in a different location, make the
appropriate path substitution.
- In the [boot] section of the file, look for a line similar to:
shell = Explorer.exe [TROJAN FILE NAME]
Note: [TROJAN FILE NAME] refers to the file name detected during
the scan.
- If this line exists, delete everything to the right of Explorer.exe.
When you are done, it should look like:
shell = Explorer.exe
- Click File > Save.
- Click File > Exit.
7. To clear the Temporary Internet Files folder, if required
- Log on to the computer using the name that was shown in the path that you
wrote down in the scan and delete infected files section.
For example, if the path was:
C:\Documents and Setting\Linda\Local Settings\Temporary Internet Files\qrwmqczd.dll
log on to the computer as Linda.
- Start Internet Explorer.
- Click Tools > Internet Options.
- In the Temporary Internet Files section, click the Delete Files
button.
- Check Delete all offline content, and then click OK.
Symantec Security Response - Trojan Horse