Threat description



Skulls.S is a variant of SymbOS/Skulls.C trojan. The component files of the trojan are almost identical to Skulls.C. The main difference is that Skulls.S drops Cabir.F several times into the same device.

If Skulls.S 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.


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.S

5. Download and install F-Secure Mobile Anti-Virus to remove any Cabirs dropped by the Skulls.S

or with mobile itself

6. Remove the F-Skulls with application manager as the phone is now cleaned

Technical Details

Installation to system

Like Skulls.A Skulls.S is a SIS file that installs critical System ROM binaries and Cabir.F and Cabir.G worms 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.

Spreading in: Liveupdate wireless.sis


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


Generic detection that detects Skulls.S was published for F-Secure Mobile Anti-Virus on December 13th, 2004 in

Detection Type: Mobile

Database: database build number 15

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