Mukund’s adventures

When I was pursuing a B.Sc. degree in Loyola Academy about 11 years ago, we used DOS and diskless machines with floppies. There was a pretty terrible virus called Die Hard 2 doing the rounds in the labs. We didn’t have a cleaner utility for this virus, and even if the McAfee SCAN.EXE and CLEAN.EXE that we had could detect and clean it (which they couldn’t anyway), they were way too slow to run. Simply loading either off a floppy into memory and program setup took a minute on those 8088 machines and then scanning took what seemed to be forever. It was during this time when I was getting better at assembly and also going through virus disassembly . I wrote a program called DH2C.COM (Die Hard 2 cleaner) in 8086 assembly which got used a lot on campus for its high speed, so much so that some people changed strings in it using a hex editor and called it their own. You could clean an entire disk in less time than SCAN.EXE took to load. This was due to DH2C’s use of file truncation and very little disk reading to check for infection.

Here is the program DH2C.COM. I seem to have lost the original source code over the years, but here is a disassembly of it. I don’t know if I can release this disassembler-generated code as free software, but the COM file is released under the modified BSD license or GNU GPLv2 and higher (no warranty, no liability). If time permits, I will comment it in the future but it should be fairly straightforward to anyone who has done DOS programming.