Virus.DOS.Kerstin.923 or Kerstin is a virus that runs on MS-DOS.
Kerstin is a non-memory resident parasitic virus.
It searches for .EXE files, then writes itself to the end of the file.
On September 16th, it plays the “Happy Birthday” tune, decrypts and displays the messages :
Kerstin.95b Happy birthday Kerstin ! I'll always be there 4 U. Contact me. In love A.