SymbOS/Cardblock.A is a trojanized version of Symbian application InstantSis created by Biscompute. The virus blocks the MMC memory card of the phone and deletes critical system and mail directories. Blocking the memory card is done by setting a random password to the card.

Some phone such as Nokia 6670 and Nokia 6600 survive from deletion of system directories quite easily, just a reboot and phone is usable. But the user data and MMC card are still lost.

Unfortunately some phones that use newer versions of Symbian OS, such as Nokia 6630 are hit harder. These phones will fail to reboot and display message that requests the phone to be taken to maintenance. However the phone can be recovered with special hard format key combination.

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