Waterfall locks requirements in up front and resists change; Agile gathers them iteratively and welcomes change every sprint.

* Waterfall locks requirements up front; Agile loops each iteration and welcomes change. *

Waterfall:

• All requirements gathered upfront
• Changes are expensive and difficult
• Works when requirements are stable and well-understood
• Sequential phases with clear milestones

Agile:

• Requirements gathered iteratively
• Changes are welcomed and expected
• Works when requirements are evolving or uncertain
• Continuous delivery of working software

Security implication:

• Waterfall: Security requirements defined early, less flexibility
• Agile: Security must be integrated into each sprint, continuous security testing

The 1988 Morris Worm was the first major internet worm; by exploiting buffer overflows in Unix services it proved such bugs could give remote code execution and take down machines network-wide.

The Morris Worm (1988) was the first major internet worm, written by Robert Morris as an experiment to estimate internet size. It spread using:

• Dictionary attacks on weak passwords
• Buffer overflow exploits in Unix services (fingerd, sendmail)

What went wrong: A bug caused it to reinfect machines repeatedly, consuming all resources and crashing ~6,000 computers (~10% of the internet at the time).

Security significance:

1. Demonstrated that buffer overflows could achieve remote code execution
2. Showed that a single vulnerability could have cascading network-wide effects
3. Led to creation of CERT (Computer Emergency Response Team)
4. First prosecution under Computer Fraud and Abuse Act

The Morris Worm proved that theoretical vulnerabilities could cause real-world catastrophic damage.

Go deeper:

• Morris worm (Wikipedia) — corroborates fingerd/sendmail exploits, ~6,000 machines, CERT, first CFAA conviction.