Blankfont.A is a SIS file trojan that installs corrupted Font file into infected device. The corrupted font does not cause device to crash, but if the device is rebooted it will lose the system font, and is unable to display user interface texts.

Any application that user tries to use after reboot works otherwise normally, but does not show any text. Which makes most of the applications unusable until the phone is disinfected.

If a phone is infected with Blankfont.A, it must not be rebooted as the trojan will corrupt system font and make disinfection quite difficult. If the phone is rebooted it can still be disinfected but, doing so is rather difficult as there is no text on the screen.

more info at f-secure

http://www.f-secure.com/v-descs/blankfont_a.shtml