Hmmmm.....
I'm no expert with computers but will throw out the following.

Does this happen with other programs on your computer?
If so, could this prompt be related to a particular anti-virus program you are using?

I just did a fresh install on Win7, haven't installed my preferred anti-virus program yet (AVG Free) and haven't had this happen to me yet when opening BIAB.
Just trying to see some logic here.

Carry on....good luck.