Copyright and software licensing

Code is intellectual property — it's a creative work fixed in a tangible medium (source files, binaries). Without copyright:

• Anyone could copy, modify, and sell your code without permission.
• No legal basis for licences (licences grant permissions that copyright withholds).
• No incentive to invest in software development.

Copyright automatically applies the moment you write code (in most jurisdictions, including UK). You don't need to register it — though registration helps enforcement.

What copyright protects: the expression (your actual code, structure, comments). What it doesn't: ideas, algorithms, functionality, interfaces (these may be patentable instead — a different regime).

A software licence is a legal document that says: "I (the copyright holder) give you permission to do X, Y, Z with my code, under conditions A, B, C."

Without a licence, all rights are reserved — no one else can legally use, copy, or modify your code.

Cambridge focuses on four licence families:

1. Free Software Foundation (FSF) / GNU — "free as in freedom"
2. Open Source Initiative (OSI) approved — includes permissive and copyleft
3. Shareware — try before you pay
4. Commercial / Proprietary — all rights reserved except what the EULA grants

1. FSF / GNU (Free Software Foundation)

• Philosophy: software freedom is a moral right.
• Key licences: GPL (General Public License) — strong copyleft. LGPL — library exception. AGPL — closes the "network use" loophole.
• If you use GPL code in your project, your whole project must be GPL (viral effect).
• Use when: you want to guarantee freedom for all downstream users.

2. OSI-approved (Open Source Initiative)

• Broader tent: includes both copyleft and permissive licences.
• Permissive: MIT, BSD, Apache 2.0 — do almost anything, just keep the licence notice. No viral effect. Business-friendly.
• Copyleft: GPL, LGPL, MPL (Mozilla Public License) — file-level copyleft.
• Use when: you want wide adoption (permissive) or community protection (copyleft).

3. Shareware

• "Try before you buy" — free evaluation period, then payment required.
• Source code usually not provided.
• No standard licence terms — each vendor writes their own.
• Use when: you want users to evaluate a commercial product.

4. Commercial / Proprietary

• Standard EULA (End User Licence Agreement): you get a limited right to use the software, not to copy, modify, reverse-engineer, or redistribute.
• Source code almost never provided.
• Support, updates, indemnity often included.
• Use when: you're selling a product and need to protect IP and revenue.