vb.net后台http下载无提示覆盖文件

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim url As String
url = "http://localhost/system.dll"

Dim path As String

path = Environment.CurrentDirectory() & "\system.dll"
Dim wc As System.Net.WebClient
wc = New System.Net.WebClient
wc.DownloadFile(url, path)

End Sub