Instalation of this antivirus :

Save the file to a convenient location, such as your Windows desktop.
Load the SymcMTRT.sis removal tool file onto the compromised device.
In the Symbian OS Menu, open the Tools folder.
Open the File Mngr. program.
Locate the SymcMTRT.sis file and open it.
Click Yes when you see the following message:

Install Symantec Mobile Threats Removal Tool?
Choose Continue and then click OK.
Click Exit to exit the file manager.
Click Back to exit the Tools folder.
Open the SymcMTRT application. 

reference : http://www.symantec.com/security_response/writeup.jsp?docid=2005-102011-2304-99