F-Secure is warning of a new malicious program for Symbian Series 60 smartphones. The program called Skulls is a malicious SIS file that will replace the system applications with non-functional versions, so that all but the phone functionality will be disabled. All application icons are replaced with the picture of a skull and cross bones.
The Skulls SIS installs modified versions of system ROM binaries into the C: drive on the smartphone, with exact same names and locations as in the ROM drive. The Symbian operating system has a feature which causes any file that is in C: drive to be invoked instead of files in ROM drive with identical names. If the Skulls program 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 will no longer work.
The program is not a virus since it lacks the ability to replicate parts of its code to another program. It relies on the user manually copying the file to try the "Extended theme". The Skulls SIS file is named "Extended theme.SIS", and it claims to be a theme manager for the Series 60 based Nokia 7610 smartphone.
F-Secure says that users who have installed the program should not restart the phone, and follow some instructions to remove the malicious code.