VBS.Freelink

SUMMARY

VBS.Freelink is an encrypted worm that works under Windows 98, Windows 2000, and all the other Windows versions that support the VBScripting language. Once the worm is launched, it uses Microsoft Outlook to automatically send an email with an attachment of itself.

Protection

• Virus Definitions (Intelligent Updater) July 8, 1999

Threat Assessment

Wild

• Wild Level: Medium
• Number of Infections: More than 1000
• Number of Sites: More than 10
• Geographical Distribution: High
• Threat Containment: Moderate
• Removal: Moderate

Damage

• Damage Level: Low
• Large Scale E-mailing: Uses MS Outlook and IRC
• Modifies Files: script.ini of Mirc32 or events.ini of Pirch32

Distribution

• Distribution Level: High
• Subject of Email: Check this
• Name of Attachment: Own filename
• Size of Attachment: 12,046 bytes
• Target of Infection: Email, IRC, drop LINK.VBS to shared network drives

TECHNICAL DETAILS

Similar to the Melissa virus, this worm uses MAPI calls to obtain user profiles from Microsoft Outlook. The email generated by this worm is:

Subject:

Check this
Have fun with these links. Bye.

When the attached file is executed, it creates the files:

C:WindowsLinks.vbs
C:WindowsSystemRundll.vbs

It also creates the file Links.vbs in the root of all mapped network drives. Next, the worm adds the value:


Rundll   RUNDLL.VBS

to the registry key:

HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun

sot that ir runs each time that Windows starts.

After infecting a system, it displays a the dialog box:

Free XXX links
This will add a shortcut to
free XXX links on your desktop.
Do you want to continue.

If you click Yes, it creates a shortcut pointing to an adult Web site.

It also searches for Mirc32.exe and Pirch98.exe in C:Mirc , C:Pirch98, C:Program Files, and in their subfolders. If it finds either of these programs, it modifies the corresponding Script.ini or Events.ini file, so that Links.vbs is sent to other people during the IRC sessions.

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

To remove this worm, you need to remove an entry that it made in the registry, and then run a full system scan, and delete files detected as VBS.FreeLink

To edit the registry:

CAUTION: We strongly recommend that you back up the system registry before making any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure you modify only the keys specified. Please see the document How to back up the Windows registry before proceeding.

1. Click Start, and then click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the following subkey:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   
4. In the right pane, delete the following value:
   
   Rundll     Rundll32.vbs
   
5. Click Registry and then click Exit to save the changes.

To remove the worm:

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and then run a full system scan, making sure that NAV is set to scan all files.
3. Delete any files detected as VBS.FreeLink.