Know which user has logged on system

how can i know through any api or vb function that which user has been logged on the system?
And is there any way to restrict a user from using any file or a folder?

Code:

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Declare Function GetUserName Lib "advapi32.dll" Alias "GetUserNameA" (ByVal lpBuffer As String, nSize As Long) As Long

Function usrName() as String
    Dim uname as string , rval as long, strlen as long
    uname = space(255)
    rval = GetUserName(uname,strlen)
    usrName = left(uname,strlen)
End Function

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Quote:

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And is there any way to restrict a user from using any file or a folder?

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You using NT/2000?

JoshT didn't mention - The answer is "no" id you're on a Win 9X machine. I don't know how to do it from code on NT. Guess I'll go figure it out....

probably by using the SetFileSecurity API, i'll look into it.