Bitcoin Core version 0.9.1 is not available for security reasons:
This is a security update. It is recommended to upgrade to this release as soon as possible.
It is especially important to upgrade if you currently have version 0.9.0 installed and are using the graphical interface OR you are using bitcoind from any pre-0.9.1 version, and have enabled SSL for RPC and have configured allowip to allow rpc connections from potentially hostile hosts.
Please report bugs using the issue tracker at github:
How to Upgrade
If you are running an older version, shut it down. Wait until it has completely shut down (which might take a few minutes for older versions), then run the installer (on Windows) or just copy over /Applications/Bitcoin-Qt (on Mac) or bitcoind/bitcoin-qt (on Linux).
If you are upgrading from version 0.7.2 or earlier, the first time you run 0.9.1 your blockchain files will be re-indexed, which will take anywhere from 30 minutes to several hours, depending on the speed of your machine.
0.9.1 Release notes
No code changes were made between 0.9.0 and 0.9.1. Only the dependencies were changed.
Upgrade OpenSSL to 1.0.1g. This release fixes the following vulnerabilities which can affect the Bitcoin Core software:
CVE-2014-0160 (“heartbleed”) A missing bounds check in the handling of the TLS heartbeat extension can be used to reveal up to 64k of memory to a connected client or server.
CVE-2014-0076 The Montgomery ladder implementation in OpenSSL does not ensure that certain swap operations have a constant-time behavior, which makes it easier for local users to obtain ECDSA nonces via a FLUSH+RELOAD cache side-channel attack.
Add statically built executables to Linux build
Credits go to the OpenSSL team for fixing the vulnerabilities quickly.