Figure 1: Incoming Virus
The worm, deemed SymbOS/Beselo.A!worm is able to run on several Symbian S60 enabled devices. These devices include, but may not be limited to, Nokia 6600, 6630, 6680, 7610, N70 and N72 phones.
After an installation phase, the worm engages in a propagation routine: phone numbers located in the contact list of the devices are harvested, and targeted by viral MMS carrying a SIS-packed (Symbian Installation Source) version of the worm. However, the SIS file does not bear a .sis file extension -- rather, it is disguised as a multimedia file with an evocative name: Beauty.jpg, Sex.mp3 or Love.rm.
Unlike Microsoft Windows, SymbianOS types files based on their content and not their extensions, so it is worth noting that recipients of infected MMS would still be presented with an installation dialogue upon "clicking" on the attachment. Therefore, users could easily be deceived by the extension and unknowingly install the malicious piece of software.
In addition to harvesting the numbers stored in the phone address book as mentioned above, the Beselo worm sends itself to generated numbers as well. Interestingly, all those numbers are located in China and belong to the same mobile phone operator. Some of those numbers have been verified to belong to actual customers, rather than being premium service numbers. The whys and hows of such a routine are still under investigation.
Figure 2: Worm Propagation
Although the prevalence of this mobile malware incident is still low, the FortiGuard Global Security Research Team will continue to monitor the situation and update the description with new findings as needed.
Users may know they have been infected if they see unrecognized sent messages in their MMS outboxes (the device needs to be configured to save such messages). FortiClient Mobile automatically detects and removes the Beselo worm. For users without FortiClient Mobile who believe they may be infected, please contact your mobile carrier or phone manufacturer for technical support in manually removing the virus.
For more information on SymbOS/Beselo.A!worm, visit the Virus Encyclopedia.
Many thanks to Dawid, the defense manager of a large, large mobile operator that has deployed our product to protect its customers from malevolent MMS messages -- and who spotted the worm first.