Threat Description

Skulls.B

Details

Aliases:Skulls.B, SymbOS/Skulls.B
Category: Malware
Type:
Platform: W32

Summary



Skulls.B is a variant of SymbOS/Skulls.A trojan, which has similar functionality to the Skulls.A but uses different files.

Skulls.B is a malicious SIS file trojan that will replace the system applications with non-functional versions and drops SymbOS/Cabir.B worm in to the phone.



Removal



Disinfection with two Series 60 phones

Download F-Skulls tool from our FTP server to your computer or to a clean phone, then:

  • 1. Install F-Skulls.sis into infected phones memory card with a clean phone
  • 2. Put the memory card with F-Skulls into infected phone
  • 3. Start up the infected phone, the application menu should work now
  • 4. Go to application manager and uninstall the SIS file in which you installed the skulls variant
  • 5. Download and install F-Secure Mobile Anti-Virus to remove any Cabirs dropped by the Skulls variant
  • http://www.europe.f-secure.com/estore/avmobile.shtml or with mobile itself http://mobile.f-secure.com
  • 6. Remove the F-Skulls with application manager as the phone is now cleaned


Technical Details



The Cabir dropped by Skulls.B does not activate automatically, but if user goes to the cabir icon in the phone menu and runs Cabir from there. The Cabir.B will activate and try to infect other phones.

The Original Skulls.B SIS file is named "Icons.SIS". Unlike Skulls.A, the Skulls.B variant does not show any pop-up messages during install (except the "Installation security warning - unable to verify supplier" message shown by the operating system).

The Skulls.B replaces standard application icons with generic application icon instead of skull and cross bones like Skulls.A did.

If Skulls.B is installed only the calling from the phone and answering calls works. All functions which need some system application, such as SMS and MMS messaging, web browsing and camera no longer function. And in addition of applications being disabled the phone is also infected with Cabir.B, which fortunately, is not able to activate automatically.

If you have installed Skulls.B, the most important thing is not to reboot the phone and follow the disinfection instruction in this description.

Installation to system

Like Skulls.A Skulls.B is a SIS file that installs critical System ROM binaries and Cabir.B worm into C: drive. The System ROM files are installed with exact same names and locations as in the ROM drive.

Symbian operating system has a feature which causes any file that is in C: drive replace file in ROM drive with identical name and location.

Unlike Skulls.A Skulls.B installs also other files than just Symbian ROM files, in the list of installed files there is Camtimer camera timer application from Nokia and Cabir.B worm binaries.

Spreading in: Icons.sis

Payload

Replaces built in applications with non-functional ones and installs Cabir.B worm.

If you have not enabled automatic updates on your antivirus or used any data connections lately, you can make sure you have the latest updates by selecting "Update Anti-Virus" from the Options menu.



Detection


Detection for this malware was published on November 29th, 2004 in the following F-Secure Anti-Virus updates:
Detection Type: PC
Database: 2004-11-19_03

Detection for F-Secure Anti-Virus for Symbian series 60 has been published at on November 29th, 2004 in
Detection Type: Mobile
Database: database build number 13



Description Created: Jarno Niemela November 29th, 2004
Description Last Modified: Jarno Niemela January 26th, 2005


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