This is a simple virus which stays resident in memory and infects COM and EXE files when they are accessed. \COMMAND.COM and \DOS\FORMAT.COM are infected on the first execution.
If you run PKZIPFIX against an infected COM or EXE file, it will create a PKFIXED.ZIP, which contains an assembly source file called ZIPPER.ASM.
The virus contains this text, which is never displayed:
>>*>> Use PKUNZIP *.EXE immediately! <<*<<