The Cascade virus is a prominent computer virus that was a resident written in assembly, and it was widespread in the 1980s and early 1990s. It infected .COM files and had the effect of making text on the screen fall down and form a heap in the bottom of the screen. It was notable for using an encryption algorithm to avoid being detected. However one could see that infected files had their size increased by 1701 or 1704 bytes. In response, IBM developed its own anti-virus software.

— Wikipedia, "Cascade (computer virus)"

• MASM 6.x
• x2b or exe2bin

cascade.asm    # source code for CASCADE virus; x86 assembly
cascade.com    # compiled, live virus
makehlv.bat    # Batch file to build virus

You can use MASM 6.11d (16bit assembler) along with X2B (EXE -> COM Converter) for building the virus. You also need DOS debug executable for patching up the initial jump (automatically done by makehlv.bat). If you are using exe2bin, you have to modify makehlv.bat accordingly.

Once you have the environment setup, follow these steps:

1. Open cascade.asm. Find DEMO EQU FALSE (it should be near line no. 13). If you make this DEMO EQU TRUE, the virus will not exhibit any harmful things. For our purpose, leave it at DEMO EQU FALSE.

2. Add _DANGER EQU TRUE after this line.

3. Execute the following command from the command-line to build the virus:

   makehlv cascade
   

This source code and instructions was obtained from Kannan's Blog