A few days ago we released version 1.6.6, unfortunately we have since realized that the version released was a newer SVN revision than intended, and as a result contains some development code that may compromise the stability of your board.
Please note that this is not a security issue, and we are not aware of any security implications arising from the release.
The issue was rectified shortly after the release and only the main release was affected, not the changed files package.
We advise anyone who used the full release package within the first 24 hours of its release to run the file verification tool in their admin control panel (Tools & Maintenance > File Verification). If any files show differences which are not manual file modifications they should be replaced with files from the current version of the release package.