Bitcoin-Qt 0.5.0 Release (Wallet Encryption)
The Bitcoin client is rebranded to Bitcoin-Qt and introduces native wallet encryption, a critical security upgrade.
On November 21, 2011, the Bitcoin development team released version 0.5.0 of the client software. This update was a massive milestone for two reasons. First, it migrated the Graphical User Interface (GUI) from the older `wxWidgets` framework to `Qt`, giving the software a much more polished, professional look. This modern interface (which is still the basis for Bitcoin Core today) made the software accessible to non-developers. Second, and most importantly, it introduced wallet encryption.
Prior to this release, the `wallet.dat` file containing a user's private keys was stored in plain text on their hard drive. Malware (like the kind that hit 'allinvain' in June) could simply copy the file and steal the funds. Version 0.5.0 allowed users to set a password that encrypted the keys, meaning a thief would need both the file and the password to spend the coins. This was a direct response to the summer of thefts and hacks that had plagued the community.
Bitcoin-Qt 0.5.0 marked the transition from 'prototype' to 'product.' It signaled that the developers were prioritizing user safety and experience, critical steps for mainstream adoption. It also introduced the `getmemorypool` RPC command, paving the way for more sophisticated mining software.
Key Sources: Bitcoin.org: Release Notes 0.5.0 | Bit2Me: What is Bitcoin Core?