A new version of OpenSSL was released 2 days ago. This version of OpenSSL is more strict about what cryptographic signatures it is willing to accept. This can cause a blockchain fork if a specialized transaction with a non-rigid transaction is added to the blockchain, or if one is already on the blockchain. For more information, see gmaxwell's post about this issue
http://sourceforge.net/p/bitcoin/mailman/message/33221963/Again, DO NOT UPDATE TO OpenSSL 1.0.0p / 1.0.1k if you compile your own wallets. Windows wallets are not affected (but developers that compile altcoin wallets for Windows need to be aware of this)
If you're an altcoin developer, please merge in the two latest commits from the Bitcoin 0.8 branch:
https://github.com/bitcoin/bitcoin/commits/0.8 (or 0.9 if your code is based on Bitcoin 0.9). This will fix the issue so that the latest OpenSSL will not cause a fork
To be specific (for most altcoins), you need to make these modifications to your code:
1.
https://github.com/bitcoin/bitcoin/commit/f4134ee30100a3ba8a25e3f7ac6c4e0b39fb05a32.
https://github.com/bitcoin/bitcoin/commit/91e1332011ca647362f95f34ae6c530640bfef98This will make it so that the new OpenSSL doesn't cause a fork
