bitcoin/bitcoin — pull request #4952 by petertodd (2014-09-20 16:35:51+00:00)
Title: Add warning about the merkle-tree algorithm duplicate txid flaw

Lots of people read the Bitcoin Core codebase to learn more about crypto; better to warn about flaws explicitly so they don't blindly copy the code for other uses and create broken systems.

Example: https://www.mail-archive.com/bitcoin-development@lists.sourceforge.net/msg06219.html