Japanese Christmas is an early DOS file virus (file infector), believed to be written in either VBS or QBasic. It was widespread in Japan (and mostly confined to that country) in 1989-1990, with variants developed as late as 1992. This virus, although very primitive when compared to later DOS viruses, utilizes very similar techniques of infection. This virus is benign, and causes no damage to software or hardware other than the risk of corruption.


When a file infected with Japanese Christmas is executed, it will infect one DOS .COM file in its directory, appending itself to the end of the file. It can infect all .com files, including COMMAND.COM. Infected files will be 600 bytes larger than their original size. The virus will not be memory-resident.

If an infected file is executed on December 25, the message "A merry christmas to you", will appear on the screen. It will flash and have an underline for about half the time it is displayed. After some time the message disappears, and will not appear again until another infected file is executed.



F-Secure, F-Secure Virus Information Pages, "Japanese Xmas".

Kaspersky Labs., Virus.DOS.Christmas.600

McAffee Threat Center. "Japanese Christmas".