Solved: ASP.NET - Concerned about File upload security

I am using the following code to upload files ...but I am concerned about security in the sense that its available to the public and I want to be sure only certain extentions can be user...txt or .csv...they are upload address info..but if a hacker comes along...they could upload a file that take over the system..any code to protect ..ideas?

FYI..the whole site has SSL on it..if that makes a difference...

<html>
<head>

    <script language="VB" runat="server">
    
    Sub Button1_Click(sender As Object, e As EventArgs)
        
        if FileUpLoad1.HasFile
            'Uncomment this line to Save the uploaded file
            'FileUpLoad1.SaveAs("C:\SomePhysicalPath" & FileUpLoad1.Filename)
            Label1.Text = "Received " & FileUpLoad1.FileName & " Content Type " & FileUpLoad1.PostedFile.ContentType & " Length " & FileUpLoad1.PostedFile.ContentLength
        else
            Label1.Text = "No uploaded file"
        end if    
        
    end sub
        
    </script>

</head>
<body>

    <h3><font face="Verdana">File Upload</font></h3>

    <form runat=server>

        <asp:FileUpLoad id="FileUpLoad1" AlternateText="You cannot upload files" runat="server" />
        <asp:Button id="Button1" Text="Upload" OnClick="Button1_Click" runat="server" />
        <asp:Label id="Label1" runat="server" />
    </form>

</body>
</html>

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