A new version of the Bitcoin-Qt and Bitcoind clients from Bitcoin.org, v0.6.3, includes a fix for a serious denial-of-service vulnerability and a performance enhancement for new installations.
http://bitcoin.org/releases/2012/06/25/v0.6.3.html (presumed, pending)
http://sourceforge.net/projects/bitcoin/files/Bitcoin/bitcoin-0.6.3
http://bitcointalk.org/index.php?topic=89877.0