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.