You don't need an antivirus for your N93. N93 is S60 3rd edition device. S60 3rd very-very secure in OS. We can't access the cage area with any of file manager app because the app must signed/registered with Symbian corp.
Virus must signed too? Symbian will kicked it !!!
You see, so far, there is no virus attacked any S60 3rd yet.
I would like to suggest you if your mobile having a virus problem so do formate your mobile with some license version anti virus because i had experience to this problem in my N95 before last two month. And avoid to online downloading with mobile Internet.