What is the Welchia.C Worm?

Welchia.C is a minor variation of, and functionally equivalent to Welchia.B. If the version of the operating system of the infected machine is Chinese, Korean, or English, the worm will attempt to download the Microsoft Workstation Service Buffer Overrun and Microsoft Messenger Service Buffer Overrun patches from the Microsoft® Windows Update Web site, install it, and then restart the computer.

The worm also attempts to remove Mydoom.A and Mydoom.B worms.

Welchia.C.Worm exploits multiple vulnerabilities, including:

• The DCOM RPC vulnerability (described in Microsoft Security Bulletin MS03-026) using TCP port 135. The worm specifically targets Windows XP machines using this exploit.Users are recommended to patch this vulnerability by applying Microsoft Security Bulletin MS03-039.
• The WebDav vulnerability (described in Microsoft Security Bulletin MS03-007) using TCP port 80. The worm specifically targets machines running Microsoft IIS 5.0 using this exploit. The worm's use of this exploit will impact Windows 2000 systems and may impact Windows NT/XP systems.
• The Workstation service buffer overrun vulnerability (described in Microsoft Security Bulletin MS03-049) using TCP port 445. Windows XP users are protected against this vulnerability if Microsoft Security Bulletin MS03-043 has been applied. Windows 2000 users must apply MS03-049.
• The Locator service vulnerability using TCP port 445 (described in Microsoft Security Bulletin MS03-001). The worm specifically targets Windows 2000 machines using this exploit.

Also known as: Nachi.worm.c, Nachi-C, Win32.Nachi.C, WORM_NACHI.C, Win32.Welchia.c

How Does the Welchia.C Worm Infect My Computer?

When Welchia.C.Worm runs, it does the actions similar to Welchia.B.Worm. Click here to see.

How to Remove the Welchia.C Worm?

Kaspersky Internet Security Can Prevent You From Virus and Intrusion. If Kaspersky detects Welchia.C during the scan, it will AUTOMATICALLY offer you the option of deleting it. Do this by following the program's instructions.

Follow these steps in removing the Welchia.C(Nachi.C) worm.

1. Disabling System Restore (Windows Me/XP)

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/XP System Restore".

2. Updating the Virus Definitions

If you do not know which anti-virus software can provide strong protection for you, Kaspersky Internet Security is recommended.

3. Identifying the Virus Program

1. Scan your system with your Kaspersky antivirus products.
2. NOTE all files detected as Nachi.C.

4. Terminating the Malware Program

1. Open Windows Task Manager.
   To do this, press
   CTRL+SHIFT+ESC(2000,XP) or CTRL+ALT+DEL(98,Me), then click the Processes tab.
2. In the list of running programs*, locate the malware file or files detected earlier.
3. Select one of the detected files, then press either the End Task or the End Process button, depending on the version of Windows on your system.
4. Do the same for all detected malware files in the list of running processes.
5. To check if the malware process has been terminated, close Task Manager, and then open it again.
6. Close Task Manager.

5. Removing the running service

1. Open a command prompt window. Click Start>Run, type CMD and then press the Enter key.
2. At the command prompt, type the following:
   NET STOP "Network Connections Sharing"
3. Press the Enter key. A message should indicate that the service has been stopped successfully.
4. Again, at the command prompt, type the following:
   NET STOP "Wkspatch"
5. Press the Enter key. A message should indicate that the service has been stopped successfully.
6. Close the command prompt window.
7. Open Registry Editor. To do this, click Start>Run, type REGEDIT, then press Enter.
8. In the left panel, double-click the following:
   HKEY_LOCAL_MACHINE>System>CurrentControlSetServices>
9. Still in the left panel, delete the subkey:
   WksPatch
10. Close Registry Editor.

6. Updating the virus definitions

If you do not know which anti-virus software can provide strong protection for you, Kaspersky Internet Security is recommended.

7. Scanning for and deleting the infected files

1. Start your Kaspersky Internet Security and make sure that it is configured to scan all the files.
2. Run a full system scan.
3. If any files are detected as infected with Nachi.C, click Delete.

How to Disinfect My Computer from Worms?

In order to keep your computer protected, bear the following tips in mind:

1. If you have filtering tools installed, configure them to reject messages with the characteristics described above. If, in spite of doing this, you receive the message that contains the virus: do not open it, do not run the attached file and delete it, making sure that you also delete it from the Deleted Items folder.
2. Install a good antivirus in your computer. Select Kaspersky Internet Security to get the Kaspersky antivirus solution that best suits your needs.
3. Keep your antivirus updated. If automatic updates are available, configure your antivirus to use them.
4. Keep your permanent antivirus protection enabled at all times.

Detect and Removal Instruction for Other Variants: