The Adobe Lightroom team issued an important announcement concerning a bug that can affect jpg users.
“The Lightroom and Camera Raw team would like to inform you of a potentially severe bug that was introduced in the Lightroom 3.4 and Camera Raw 6.4 update. Please note that this bug only impacts customers who are saving metadata to JPEG files with a rare characteristic.(JPEG files must have an unusually large block of private camera data included in the file to be susceptible to the bug*) This scenario is so rare that we do not believe that it is necessary for customers who have already upgraded to revert to the previous version of Lightroom or Camera Raw. However, the bug could cause image corruption which falls within our highest severity category of bugs. The team believes it’s very important to notify you of the risk and provide an estimate of when we will be able to deliver a correction in the form of Lightroom 3.4.1 and Camera Raw 6.4.1. We intend to have these updates available by Friday, May 27th.”