From the GETH team:
This release improves block processing performance to work around recent DoS attacks. It also disables the –jitvm A/B test which previously enabled the experimental JIT VM for 10% of geth users.
The DoS issue that began affecting the ethereum network two days ago has been remediated by adding state journalling to Geth. Journalling means that we no longer need to copy a transaction’s state when a call is made; this is the root cause of many of the recently identified issues. Journalling, along with other recent improvements in response to other attacks, should also make Geth significantly faster at importing transactions.