Bitcoin version 0.6.3 is now available for download at: http://sourceforge.net/projects/bitcoin/files/Bitcoin/bitcoin-0.6.3/
This is a bug-fix release, with no new features.
Please report bugs using the issue tracker at github: https://github.com/bitcoin/bitcoin/issues
Fixed a serious denial-of-service attack that could cause the bitcoin process to become unresponsive. Thanks to Sergio Lerner for finding and responsibly reporting the problem. (CVE-2012-3789)
Optimized the process of checking transaction signatures, to speed up processing of new block messages and make propagating blocks across the network faster.
Fixed an obscure bug that could cause the bitcoin process to get stuck on an invalid block-chain, if the invalid chain was hundreds of blocks long.
Bitcoin-Qt no longer automatically selects the first address in the address book (Issue #1384).
Fixed minimize-to-dock behavior of Bitcoin-Qt on the Mac.
Added a block checkpoint at block 185,333 to speed up initial blockchain download.