Threat description



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

Skulls.M is a malicious SIS file trojan that replaces the system applications with non-functional versions and disables third party applications that could be used to disinfect with such as FExplorer and System Explorer.

Like Skulls.A the Skulls.M replaces the application icons with it's skull icon, this time so that each replaced application has caption "Khalid"

If Skulls.M 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.

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


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

Technical Details

Installation to system

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

Spreading in: X-Ray Full byDotSis.SIS


Replaces built in and third party applications with non-functional ones.


Generic detection that detects Skulls.M was published for F-Secure Mobile Anti-Virus on November 19th, 2004 in

Detection Type: Mobile

Database: database build number 11

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