Some scheduled virus definitions updates are failing, but others are succeeding at least once a day and manual updates also work.
"There was an error running content update, scanning will continue using the original definitions"
Incremental virus definition updates are currently failing due to an indexing problem.
Full virus definition updates are working correctly, so SPE will still update all it's definitions at least once a day. Manual updates can be run as required and they will also work.
This issue has been resolved as of 05/05/2014. The index has been modified to prevent the problem from occurring. This should occur automatically. In the event that the issue continues, please contact Technical Support.