Did you ever wonder why the UAC prompt in Windows Vista takes a really long time to start your big installation package? The reason is simple. The UAC application copies the whole file into a temorary folder to elevate it from there. This process needs a lot of time. Why? I suspect the following security risk: A bad guy could replace the application file with another one while you read the UAC prompt message. Renaming a file even works if the file is in use. So a bad guy just have to rename two files (e.g. myBigApp.exe -> myBigApp._xe and myBadApp.exe -> myBigApp.exe) to make it work.

So it is not a good idea to create a big installation application since there won’t be any progress indication. What would be a good solution? At least two files: the install application and the data file.