https://bitcoinfoundation.org/blog/?m=201402
Quote
Gavin Andresen Feb 11 2014
You may have noticed that some exchanges have temporarily suspended withdrawals and wondering what’s going on or more importantly, what’s being done about it. You can be rest assured that we have identified the issue and are collectively and collaboratively working on a solution.
Somebody (or several somebodies) is taking advantage of the transaction malleability issue and relaying mutated versions of transactions. This is exposing bugs in both the reference implementation and some exchange’s software.
We (core dev team, developers at the exchanges, and even big mining pools) are creating workarounds and fixes right now. This is a denial-of-service attack; whoever is doing this is not stealing coins, but is succeeding in preventing some transactions from confirming. It’s important to note that DoS attacks do not affect people’s bitcoin wallets or funds.
Users of the reference implementation who are bitten by this bug may see their bitcoins “tied up” in unconfirmed transactions; we need to update the software to fix that bug, so when they upgrade those coins are returned to the wallet and are available to spend again. Only users who make multiple transactions in a short period of time will be affected.
As a result, exchanges are temporarily suspending withdrawals to protect customer funds and prevent funds from being misdirected.
Thanks for your patience. Follow us @BTCFoundation for updates as we learn more and make progress.
You may have noticed that some exchanges have temporarily suspended withdrawals and wondering what’s going on or more importantly, what’s being done about it. You can be rest assured that we have identified the issue and are collectively and collaboratively working on a solution.
Somebody (or several somebodies) is taking advantage of the transaction malleability issue and relaying mutated versions of transactions. This is exposing bugs in both the reference implementation and some exchange’s software.
We (core dev team, developers at the exchanges, and even big mining pools) are creating workarounds and fixes right now. This is a denial-of-service attack; whoever is doing this is not stealing coins, but is succeeding in preventing some transactions from confirming. It’s important to note that DoS attacks do not affect people’s bitcoin wallets or funds.
Users of the reference implementation who are bitten by this bug may see their bitcoins “tied up” in unconfirmed transactions; we need to update the software to fix that bug, so when they upgrade those coins are returned to the wallet and are available to spend again. Only users who make multiple transactions in a short period of time will be affected.
As a result, exchanges are temporarily suspending withdrawals to protect customer funds and prevent funds from being misdirected.
Thanks for your patience. Follow us @BTCFoundation for updates as we learn more and make progress.