Gavno, spreads via a file called patch.sis and disrupts Symbian-based mobiles to such an extent that users are no longer able to make phone calls.
"The Ganvo trojan is a significant development," said Aaron Davidson, CEO at anti-virus firm SimWorks. "Gavno is just 2kb in size, effectively making it the most destructive and the smallest trojan at the same time."
Both Gavno.a and Ganvo.b variants have been identified. The second version also includes a copy of the Cabir trojan, the original mobile phone threat.
Gavno works by using a malformed file to crash an internal Symbian process. Once infected it is very difficult to save the mobile phone.
Fortunately the virus is not yet spreading in the wild and still requires some user interaction to enable it. But unlike other mobile phone viruses that openly declare themselves Gavno masquerades as a patch.
"With this continuing we're getting near the stage where everyone will have to start getting anti-virus on their mobiles," said David Emm, senior technology consultant at anti-virus firm Kaspersky.
2005 has already been a bumper year for mobile phones viruses with the continuing spread in the wild of the Cabir and Skulls trojans. Virus writers tap in to the vulnerability of phones using roaming Bluetooth connections.