Posted by In the world of programming, few things spark as much fascination — and fear — as self-modifying code. Imagine a program that, every time it runs, rewrites itself. Not just superficially, but deeply enough that its very structure mutates, while the final output remains unchanged.
Welcome to the world of metamorphic programming.
Today, we’ll explore how we built a Python-based Metamorphic Code Engine, that mutates its own source code during execution. We’ll dive deep into how it works, why it matters, real-world uses (including both ethical and malicious ones), and what it teaches us about the future of software.
What is Metamorphic Programming?
Metamorphic programming is the concept where a program actively changes its internal structure without altering its functionality. The code essentially “evolves” over time, reordering logic, inserting junk code, and modifying variable names.
This idea is heavily inspired by metamorphic viruses in cybersecurity — malware that mutates its own code on each infection, making it incredibly hard for antivirus software to detect.
Key characteristics:
- Changes its own source code
- Output or functionality remains unchanged
- Introduces randomness (e.g., new variable names, useless code blocks)
- Difficult to statically analyze or detect
Why Metamorphic Programming Matters
- Evasion: In cybersecurity, it shows how difficult it can be to detect threats that don’t have static signatures.
- Obfuscation: Protects intellectual property by making reverse-engineering harder.
- Evolutionary Computing: Lays the foundation for self-evolving software.
- Education: Helps researchers and students learn about code structure, compilers, and detection techniques.
What We Built: Metamorphic Code Engine
We developed an educational Python tool that mutates its own source every time it runs.
Features:
- Randomized variable names
- Random junk line insertion (no-ops)
- Logic block shuffling
- Same program behavior after mutation
- Lightweight and easy to understand
The Core Code (engine.py)
Here’s a minimal look at the core engine.py:
import random
import string
import os
class MetamorphicEngine:
def __init__(self, filename):
self.filename = filename
def random_var(self):
return ''.join(random.choices(string.ascii_lowercase, k=random.randint(4, 8)))
def junk_line(self):
return random.choice([
f'{self.random_var()} = {random.randint(0, 100)} # junk',
f'{self.random_var()} = "{random.choice(["hello", "test", "no-op"])}" # junk',
'pass # junk',
'# this does nothing',
f'if {random.randint(0, 1)} == {random.randint(0, 1)}: pass # junk'
])
def mutate_code(self, logic_blocks):
random.shuffle(logic_blocks)
final_code = ['import random', 'import string', '']
for block in logic_blocks:
final_code.append(self.junk_line())
final_code.append(block)
final_code.append(self.junk_line())
return '\n'.join(final_code)
def write_mutated(self, logic_blocks):
new_code = self.mutate_code(logic_blocks)
with open(self.filename, 'w') as f:
f.write(new_code)
This is the heart of the mutation: junk insertion, logic reordering, and self-rewriting.
Example Payload (hello_world.py)
if __name__ == '__main__':
from engine import MetamorphicEngine
import os
v1 = 'greeting'
v2 = 'target'
v3 = 'message'
logic_blocks = [
f'{v1} = "Hello"',
f'{v2} = "World!"',
f'{v3} = {v1} + ", " + {v2}',
f'print({v3})'
]
filename = os.path.abspath(__file__)
engine = MetamorphicEngine(filename)
engine.write_mutated(logic_blocks)
Every time hello_world.py runs, it rewrites itself with junk code and shuffled logic, yet still prints “Hello, World!”.
Non-Virus Uses of Metamorphic Techniques
Even though metamorphic techniques are famous for malware, they can be used ethically too:
- Software Protection: Obfuscate proprietary algorithms from reverse engineers.
- Evolutionary Algorithms: Create programs that evolve their structure to solve optimization problems.
- Digital Art: Make art that evolves its own code.
- CTF Challenges: Build security puzzles where the source itself fights the solver.
- Resilience: Write resilient systems that adapt their internal code to survive environmental changes.
How Common Are Metamorphic Viruses Today?
Metamorphic malware is rare but very dangerous.
Examples include:
- Simile (early 2000s)
- ZMist/ZipMastah (famous for self-insertion)
- W32.Evol
Why rare?
- Very hard to write
- Extremely complex and buggy
- Signatureless detection isn’t perfect, but AI/ML-based antivirus has caught up
Today, cybercriminals often prefer simpler techniques like polymorphism (changing encryption keys) or obfuscators, but truly metamorphic malware still represents an “elite tier”.
Could Metamorphic Engines Be Turned into a Virus?
Technically, yes. If you replace the payload with malicious behavior (spying, stealing files, spreading), then add propagation features, you could turn a metamorphic engine into malware.
BUT: This project is strictly educational. Our goal is to understand, not to harm.
Ethical usage always matters.
Conclusion
Metamorphic programming is our dive into a world where code doesn’t stay still. Instead, it lives, breathes, and evolves — much like biological organisms.
Metamorphic programming challenges us to think differently about static codebases, about software resilience, about AI, and even about security itself.
Whether for defense, creativity, or just pure fascination, learning how programs can change themselves is a thrilling journey. This is just the first step.
Call to Action
- Try it yourself: Fork the metamorphic engine, create your payloads, and watch them mutate.
- Share your experiments: Can you make code poetry that evolves? Maybe even self-healing software?
- Stay ethical: Always use self-modifying code responsibly.
The future belongs to living, adapting code. Let’s create it together.
Spyboy blog 