Trojan:SymbOS/Skulls.D is a malicious SIS file trojan, that pretends to be Macromedia Flash player for Symbian Series 60 devices.
Instead, the trojan replaces system ROM binaries related to application uninstall and Bluetooth control. It also drops Cabir.M and other applications, disables third party file managers and tries to disable F-Secure Mobile Anti-Virus.
Fortunately, the Cabir.M worm in Skulls.D's payload is already detected with generic detection as Cabir.Gen; this results in Skulls.D being detected and stopped without needing an updated Anti-Virus database. Note that for this to occur, F-Secure Mobile Anti-Virus must be in realtime scan mode, as it is by default.
If you have installed Skulls.D, the most important thing is not to reboot the phone and follow the disinfection instruction in this description.
Skulls.D has been found both as independent SIS file, and as an embedded SIS in which the host SIS file pretends to contain cracked game or application.
Unlike earlier Skulls versions the Skulls.D disables only few phone system applications. The only system applications that are disabled are the ones that are needed in disinfecting it.
Skulls.D also tries to disable third party applications the user would need to disinfect the phone of a Skulls infection. For some reason however, Skulls.D copies the replacement files to the device memory card, thus disabling the tools only if user has not installed them on the C: drive.
Skulls.D is designed to disable F-Secure Mobile Anti-Virus by replacing its files with non-functional versions. As the Anti-Virus detects the infected SIS file and prevents it from being installed, this does not occur.
The Cabir.M dropped by Skulls.C does not activate automatically, but will activate on reboot. The Skulls.D does also drops other applications that will activate on device reboot. This application displays animation of flashing Skull picture on background, no matter what application user is trying to use: