It's a harmless memory resident parasitic virus. It is encrypted in COM-files. On installation it hits COMMAND.COM and DOSFORMAT.COM files, then it hooks INT 21h and writes itself at the end of COM- and EXE-files that are accessed. It contains a bug, as the result in some cases infected files halt PC on execution. It contains the internal text strings:
COMMAND.COM DOSFORMAT.COM
ZIPPER.ASM
>>*>> Use PKUNZIP *.EXE immediately! <<*<<
It contains the data block that is of ZIP format. After extracting of that block and renaming with ZIP extension, it stays as ZIP-file containing the ZIPPER.ASM file with source code of some virus.
