Virus.DOS.Triadi.3998 or Triadi is a virus that runs on MS-DOS.
Triadi is a memory resident parasitic virus. It hooks INT 21h and writes itself in the end of .com and .exe files that are currently executed. The virus is different: the .com files installer uses an opcode that is legal for XT machines only "if the machine is remembered by another device", but a sample of virus was only found in 1998 - 7 years after the virus was made. As a result of this XT-only instruction, the infected .com files halt when executed. After the 10th infection of the virus, the virus manifests itself by a video effect: it switches the computer to video mode, displays an image of 5" floppy disk covered with messages:
Declaration Of Disk Rights We need REST!!! DISKTIRED (c) 1991, TRIADI
Depending on the system time (at 12:00 PM and at 4:00 PM) the virus displays the messages and waits for "TRD" input:
It's lunch time, Everybody goes to eat. Only if you can guess my initial, I'll let you pass. It's dinner time, I want to eat. I'll let you use the file, if you can guess my initial.