VB 3.5 Check If File Is In Use

I have an update program that is completely independent of my main application. I run the update.exe to update the app.exe. To check to see if the file is in use, I move it to another file and catch an error if it is in use. If no problems occur I rename it back. At least that was my plan.

Main program: app.exe
Update program: update.exe

This program is used over the network without any services running. So, the users is quite literally running the exe over the network on their machine. I need to update the app.exe when the update.exe has run. To check to see if the app.exe was still in use I was wrapping the following in a try/catch to see if it failed:

IO.File.Move(upddir & "app.exe", upddir & "app.exe.tst")
IO.File.Move(upddir & "app.exe.tst", upddir & "app.exe")

The funny thing is, even if the app.exe is running, the move can rename it to the app.exe.tst without any error. I can even continue on in the application without any errors. I thought I was out of my mind, so I had another programmer look at this and he verified what I said above. So, we tried this wrapped in a try catch: [Code] I put the fileshare as none that, at least I thought it would, show that there was someone in the file. It still continued without any error. Anyone know why I can rename a file in use? Also, is there a better way to do this than what I am doing now?