Backdoor.Assasin.B

Symantec Security Response - Backdoor.Assasin.B

Backdoor.Assasin.B is a backdoor Trojan that gives an attacker unauthorized access to an infected computer. By default it opens port 6969. The Trojan attempts to disable some antivirus and firewall programs by terminating the active processes.

Also Known As: Backdoor.Assasin.11 [AVP], Backdoor-AGS [McAfee], BKDR_SANISI.A [Trend]
Type: Trojan Horse
Infection Length: 216,064 bytes
Systems Affected: Windows 95, Windows 98, Windows Millenium, Windows NT, Windows 2000, Windows XP
Systems Not Affected: Windows 3.x, Microsoft IIS, Macintosh, Unix, Linux

technical details

Backdoor.Assasin.B is a variant of Backdoor.Assasin. When Backdoor.Assasin.B runs, it performs the following actions:

It displays the message "Please open IP_Grabber now!"

It copies itself as %windir%\Ms spool32.exe.

Next, it creates the file %windir%\Ms spool32.dat. This file is not viral. It contains a list of various antivirus and firewall programs that the Trojan will attempt to terminate.

NOTE: %windir% is a variable. The Trojan locates the Windows installation folder (by default this is C:\Windows or C:\Winnt) and uses it as a destination folder.

The Trojan creates the value

Ms Spool32 %windir%\ms spool32.exe

in the registry key

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

so that the Trojan starts when you start Windows.

It also creates these registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\AUFOBK
HKEY_LOCAL_MACHINE\SOFTWARE\AUFOBK\eu%t{efn74+fzb]

NOTE: The Trojan uses these registry keys to store configuration information in an encoded form. For this purpose, the Trojan creates several values in these keys.

The Trojan attempts to disable some antivirus and firewall programs by terminating the active processes.

If the operating system is Windows 95/98/Millenium, the Trojan registers itself as a service process, so that it continues to run after you log off. In this case, Backdoor.Assasin.B closes only when you shut down the system.

The Trojan can install hook procedures into a hook chain to monitor the system for any keyboard and mouse input. The keyboard and mouse hook procedures process the messages and pass the hook information to the next hook procedure in the current hook chain. This permits Backdoor.Assasin.B to intercept keystrokes. For this purpose the Trojan may drop and use a .dll file that is detected by Symantec antivirus products as PWS.Hooker.Trojan.

It uses ICQ pager and/or email to notifies the client side.

After Backdoor.Assasin.B is installed, it waits for commands from the remote client. The commands allow the hacker to perform the following actions:

• Deliver system and network information to the hacker.
  Open and close the CD-ROM drive and perform other annoying actions.
  Intercept confidential information by capturing keystrokes.
  Compromise the security settings of Internet Explorer.
  Change the Internet Explorer home page so that it opens to Web sites that have potentially unsafe contents which might be activated if the security settings were compromised.

removal instructions

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.
2. Do one of the following:
Windows 95/98/Millenium: Restart the computer in Safe mode.
Windows NT/2000/XP: End the Trojan process.
3. Run a full system scan, and delete all files that are detected as Backdoor.Assasin.B or PWS.Hooker.Trojan.
4. Remove the value that the Trojan added to the registry key

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

To reverse the changes that the Trojan made to the registry:

CAUTION: Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.

1. Click Start, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the key

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

4. In the right pane, delete the value

Ms Spool32 %windir%\ms spool32.exe

5. Exit the Registry Editor.

NOTE: You may need to reinstall your antivirus or firewall product.