Either make the selections in Search to look in system and hidden folders
or set Folder Options> view to show all files and to *not* hide system
protected files. Then search for the file. It's location or Properties may
give clues about what it is and what it does.
As it stands, a search on Google does not find a file by that name. Many
hits on just "vdac" but no definitive information as this is an acronym
used in many fields. Most of the computer related references were about
writing code for drivers of various types.
I believe that VDAC.exe is the Nextel Desktop Assistant that is used
for synchronizing your email and contacts to your Nextel phone. Try
downloading the latest version from Nextel.
