Security alert [Implementation of BLOCKHASH instruction in C++ and Go clients can potentially cause consensus issue – Fixed. Please update.]

A security vulnerability in BLOCKHASH implementation affected Ethereum clients geth (versions up to 1.1.3 and 1.2.2) and eth (versions prior to 1.0.0), potentially causing consensus issues and chain reorganization. The bug has been fixed and users are advised to update their clients immediately.