With the new release of Joomla 1.5.18 comes a new release of the (free!) Version Verification Tool. This new update allows you to verify the integrity of all Joomla releases from 1.5.0 to 1.5.18. Great as a sanity check for possible hacking/modification attempts. VVT also makes upgrading less stressful as you move to 1.5.18, as you can be sure that no modifications have been made that will be overwritten.