Is Your Repackaged MSI Foul-Proof?

The art of converting a legacy installation into a Windows installer package is known to many. And accepting the vendor repackaging tool's output, a standard practice. While we can create an msi package through the reverse engineering process of repackaging, we are often content with making sure the application works and passes the user acceptance test. But is that enough to ensure that the msi package is foul proof?