These are dangerous parasitic viruses which hit by standard way .COM-files of current directory. The viruses are not memory resident but create a memory resident program which hooks INT 17h and exchanges the symbols that are output to printer. The texts "V1" and "*.COM" are present at the virus beginning.
Fumble.867
After execution of an infected file it leaves a small memory-resident program in the memory. This routine substitutes some characters typed in from the keyboard. When infected files are run the virus hooks INT 16h, 20h, 21h.
