These are very dangerous memory resident encrypted parasitic viruses. They hook INT 21h and write themselves to the end of .COM files (except COMMAND.COM) that are executed or accessed by FindFirst/Next DOS functions. The virus have bugs and often corrupt files while infecting them. Depending on the system time they overwrite files with the text:
"Dof.983": RAVEL - BOLERO
"Dof.962,1000.b": RAVEL - Carmen
"Dof.1000.a": divide overflow
"Dof.1294": Divide Overflow
The viruses also contain the texts:
"Dof.1000.b": BUCURESTI 1994.
