Which malware type overwrites the host's code completely or partially with viral code?

• A. Intrusive viruses
• B. Transient virus
• C. TSR virus
• D. Worms

Answer: (A)

The question tests how a virus can affect a program by replacing its instructions. Overwriting the host’s code means the virus writes over all or parts of the original executable with its own code, so when the program runs the virus executes instead of the original logic. This is the defining behavior of intrusive viruses: they replace or partially replace the host code to ensure the viral payload runs with each execution, often destroying or corrupting the original program in the process.

Transitory or TSR viruses focus on memory residence and reinfection behavior rather than permanently replacing the host file’s code. Worms, on the other hand, are standalone programs that spread across networks without needing to modify a host executable’s code.