Skulls.L is a variant of SymbOS/Skulls.C trojan. The component files of the trojan are almost identical to Skulls.C. The main difference between Skulls.L and Skulls.C is that Skulls.L pretends to be a pirate copied version of F-Secure Mobile Anti-Virus.
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Please note that while Skulls.L original filename is the same as F-Secure Mobile Anti-Virus Skulls.L does not contain functional pirate copied version of Mobile Anti-Virus. Skulls.L does contain files with same names as F-Secure Mobile Anti-Virus, but these files are heavily truncated versions of real files.
The real F-Secure Mobile Anti-Virus should be downloaded only from official F-Secure servers, and the correct installation SIS package is Symbian signed, so you can verify the source.
So if you are trying to install something that shows following warning, abort the installation.
Skulls.L is a malicious SIS file trojan that replaces the system applications with non-functional versions, drops SymbOS/Cabir.F and Cabir.G worms in to the phone and disables third party applications that could be used to disinfect with such as FExplorer, EFileman.
The Cabir.F and Cabir.G worms dropped by Skulls.L are already detected.
Skulls.L tries to disable F-Secure Mobile Anti-Virus by replacing it's files with non-functional versions. However as F-Secure Mobile Anti-Virus is capable of detecting Skulls.L using generic detection. The Anti-Virus will detect the infected SIS file and prevent it from being installed. Provided that the Anti-Virus is in realtime scan mode as it is by default.
The Cabir.F and Cabir.G dropped by Skulls.L does not activate automatically, and will not activate on reboot. The only way the dropped Cabir worms can activate is if user goes to the icon of the dropped Cabir file and run it from there.
When installed Skulls.L displays following message
"F-Secure Antivirus protect you against the virus. And don`t forget to update this!"
Like Skulls.A the Skulls.L replaces the application icons with skull icon, this time so that each replaced application has caption "Skulls"
If Skulls.L 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.L, the most important thing is not to reboot the phone and follow the disinfection instruction in this description.
Like Skulls.A Skulls.L 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: F-secure_Antivirus_OS7.sis
Replaces built in applications with non-functional ones and installs Cabir.F and Cabir.G worms.