W95.Tenrobot.C

SUMMARY

W95.Tenrobot.C is a memory-resident, file-appending virus. It is a variant of W95.Tenrobot. This virus only infects files when it is executed on a Windows 95/98/Me system.

W95.Tenrobot.C also attempts to give its creator unauthorized access to an infected computer through IRC.

NOTE: Definitions dated prior to June 6, 2003 may detect this threat as Bloodhound.W32.1.

Protection

• Virus Definitions (LiveUpdate™ Weekly) June 11, 2003
• Virus Definitions (Intelligent Updater) June 10, 2003

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

W95.Tenrobot.C performs similar actions as W95.Tenrobot. The differences are:

• Part of W95.Tenrobot.C is encrypted.
• W95.Tenrobot.C attempts to connect to an IRC server on 195.117.228.107, using port 6667.

For more information, refer to the W95.Tenrobot writeup.

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

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions.
2. Remove the virus, by performing one of the following:
   • Windows NT/2000/XP: Run a full system scan and repair the files detected as W95.Tenrobot.C. (First re-install your Symantec antivirus product, if necessary.)
   • Windows 95/98/Me: Restart the computer using a Rescue disk, and then run a scan.
     

For specific details on each of these steps, read the following instructions.

1. Updating 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 the Virus Definitions (LiveUpdate).
• 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.

2. Removing the virus

Windows NT/2000/XP

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   
   NOTE: If your Symantec antivirus product crashes when you start it, re-install it.
   
   • 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."
2. Run a full system scan.
3. If any files are detected as infected with W95.Tenrobot.C, click Repair.

Windows 95/98/Me
Because the virus remains in memory, restart the computer using a Rescue disk.

NOTE: These instructions pertain to Norton AntiVirus consumer products. If you are using an enterprise product such as Symantec AntiVirus Corporate Edition, contact Symantec Technical Support.

CAUTION: The Rescue Disk set must have current definitions. If you do not have a current Rescue Disk set, create one on an uninfected computer.

NOTE: If the infected computer uses a drive-compression utility or Dynamic Drive Overlay (DDO), refer to the document, "How to repair a virus when using a dynamic drive overlay or a disk compression utility," before continuing.

1. Close all the programs on the infected computer, and then turn off the power. (You must turn off the power to clear memory.)
   
   
2. Wait at least 30 seconds.
   
   
3. Insert the "Basic Rescue Boot Disk" into the floppy disk drive. Restart the computer.
   
   
4. When the Rescue Disk window appears, use the arrow keys on the keyboard to select Norton AntiVirus.
   
   
   
   
   
   CAUTION: Make sure that you select Norton AntiVirus when using a Rescue Disk that was created on another computer. Failure to do so could overwrite critical files and prevent the computer from starting.
   
   
5. On the command line at the bottom of the window, edit the line to read: navdx /cfg:a /a /doallfiles /repair.
   
   
   
   
   
   and then press Enter.
   
   NOTE: This will cause Norton AntiVirus to repair the infected files without prompting. If you want to be prompted when an infected file is found, use the command: navdx /cfg:a /a /doallfiles /prompt.
   
   
6. Follow the prompts and remove and insert the disks as necessary. You may need to do this several times. Press Enter after inserting each disk.
   
   
7. When the scan has finished (this process could take several hours), the removal process is complete. Remove all the disks from the disk drives, and then turn off the computer. Wait at least 30 seconds before restarting the computer.