NightKing virus (1997) stores the current time in the MBR of the hard drive, and one month after infecting the virus reads to the memory the FAT of the C: drive, then corrupts the FAT, displays the message:
+-----------------------------------------------+ ¦ Hello dear friend, your computer is attacking ¦ ¦ by NIGHT KING I. virus. If do you like your ¦ ¦ data very much, don't reset your computer ¦ ¦ before midnight ! ¦ +-----------------------------------------------+
then the virus waits till midnight and restores the corrupted data. If the computer is rebooted before midnight the FAT is lost.