User name VB

I have a user who is attempting to put together a vb script that collects the name of the user logged into a system when they open up a specific file located on a network drive. Currently he is scraping the name based on the name entered in the application (Office), which doesn’t always reflect the truth or match the username known by the system. He was thinking of getting information from the registry, but may not be able to access it directly. Any thoughts?