W32.HLLP.Lassa

SUMMARY

W32.HLLP.Lassa is written in Visual Basic. It prepends itself to host files and appends randomly chosen bytes to the end of the host files. It may also overwrite the host file with the pure viral code.

Protection

• Virus Definitions (LiveUpdate™ Weekly) July 17, 2002
• Virus Definitions (Intelligent Updater) July 15, 2002

TECHNICAL DETAILS

When W32.HLLP.Lassa runs, it does the following:

It inserts the following text into the C:WindowsWin.ini file:
[windows]
run=C:<the virus file name>

It may also insert the following text into C:WindowsSystem.ini:
[boot]
SCRNSAVE.EXE=C:<the virus file name>

It randomly creates some files that are pure viral code. Those files are all 40,960 bytes in length. The file names can be

• C:\%system%Sex.exe
• C:\%system%Sex.scr
• C:\%windir%Nude.scr
• C:\%windir%Nude.exe

NOTES:
%windir% is a variable. The virus locates the Windows folder (by default this is C:Windows or C:Winnt) and copies itself to that location.
%system% is a variable. The virus locates the System folder (by default this is C:WindowsSystem or C:WinntSystem32) and copies itself to that location.

The virus randomly chooses some .exe or .scr files as host files; it then copies the host files to new files as <original file name>.tmp and prepends 40,960 bytes of pure viral code to the host files. It may also append some random bytes to the end of the host files. For example, if the host file is C:WindowsMplayer.exe, the virus copies this original host file as C:WindowsMplayer.tmp.

NOTE: The virus can infect the same file several times; thus the .tmp file copies may also be infected.

It may also overwrite the host files with 40,960 bytes of pure viral code.

Recommendations

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.

REMOVAL

NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions, run a full system scan, and delete all files that are detected as W32.HLLP.Lassa.
2. On Windows 95/98/Me computers, remove the lines that the virus added to the Win.ini and System.ini files.

For details on how to do this, read the following instructions.

To scan for and delete the infected files:

1. Obtain the most recent virus definitions. There are two ways to do this:
   • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
   • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.
     
     Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
2. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
   • Norton AntiVirus Consumer products: Read the document How to configure Norton AntiVirus to scan all files.
   • Symantec Enterprise antivirus products: Read the document How to verify a Symantec Corporate antivirus product is set to scan All Files.
3. Run a full system scan.
4. If any files are detected as infected by W32.HLLP.Lassa, click Delete.

To remove the lines from the Win.ini and System.ini files
This section applies only to computers that are running Windows 95/98/Me.

NOTE: (For Windows Me users only) Due to the file-protection process in Windows Me, a backup copy of the file that you are about to edit exists in the C:WindowsRecent folder. Symantec recommends that you delete this file before you continue with the steps in this section. To do this using Windows Explorer, go to C:WindowsRecent, and in the right pane select the Win.ini file and delete it. It will be regenerated as a copy of the file that you are about to edit when you save your changes to that file.

1. Click Start, and click Run.
2. Type the following line, and then click OK.
   
   edit c:windowswin.ini
   
   The MS-DOS Editor opens.
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
3. In the [windows] section of the file, look for an entry similar to the following:
   
   run=C:<the virus file name>
   
4. If it exists, select the entire line. Be sure that you have not selected any other text, and then press Delete.
5. Click File, and click Save.
6. Click File, and click Exit.
7. Click Start, and click Run.
8. Type the following line, and then click OK.
   
   edit c:windowssystem.ini
   
9. In the [boot] section of the file, look for an entry similar to the following:
   
   SCRNSAVE.EXE=C:<the virus file name>
   
10. If you find it, select the entire line. Be sure that you have not selected any other text, and then press Delete.
11. Click File, and click Save.
12. Click File, and click Exit.