4k is a computer virus which infects COM files and EXE files.
The virus was one of the first to employ stealth tactics. Infected systems will hang, after September 22 every year, which is also the date of birth Bilbo Baggins (The Lord of the Rings).
The code was intended to display the message “Frodo Lives”, but hangs in all known variants. This virus was spread without the aid of the Internet. It was ported between systems by floppy disks.