Sophos said on Wednesday that a 32-year-old Brazilian programmer has published the source code for the Cabir-H and Cabir-I viruses online and said it could be used by virus writers to create their own variants.
This follows reports on Tuesday that a number ofand that these offshoots have evolved beyond their . The worm affects phones running the Symbian operating system that use Bluetooth wireless technology.
"Publishing virus source code on the Web is dangerous because it encourages others to create malware," Graham Cluley, senior technology consultant at Sophos, said in a statement.
The Brazilian programmer claims to have written the worms from scratch because so many people had contacted him asking if he had the source code for the, according to Sophos.
Cluley said people should be cautious about installing applications on their cell phone, as more viruses may be written, now the code is freely available.
"Although viruses for mobile phones have to date been creating more hype than havoc, it's possible that more malicious people will now be investigating ways to infect cell phones. All users should be very careful about what applications they allow to install and run on their mobile device."
Symbian phone users can protect themselves by turning off the phone's "discoverable" mode, Sophos said. It said it has not yet received a report from a member of the public with a cell phone infected by a virus.
The malicious software affects only Symbian OS-based phones running Nokia's Series 60 user interface, according to Symbian.
Ingrid Marson of ZDNet UK reported from London.