Mediafire bot

Imports System.Threading, System.Net, System.IO
Public Class Form1
    Dim T As New Thread(AddressOf StartBot)
    Dim Started As Boolean = False
    Delegate Sub AddListViewItem(ByVal username As String, ByVal password As String)
    Dim HoolLVI As New AddListViewItem(AddressOf ALVI)

    Sub ALVI(ByVal username As String, ByVal password As String)
        If Me.InvokeRequired Then
            Invoke(New AddListViewItem(AddressOf ALVI), username, password)
        Else
            Dim LVI As New ListViewItem(username)
            LVI.SubItems().Add(password)
            ListView1.Items.Add(LVI)
        End If
    End Sub
    Sub StartBot()
        Do
            Try
                Dim username As String = GenerateString(7, 0, 0) & "@gmail.com"
                Dim password As String = GenerateString(7, 0, 0)

                If New WebClient().DownloadString("https://www.mediafire.com/api/user/register.php?application_id=1000&email=" & username & "&password=" & password & "&version=1").Contains("Success") Then
                    ALVI(username, password)
                End If

                FlatLabel8.Text = String.Format("Accounts[ " & ListView1.Items.Count & "]")
            Catch ex As Exception

            End Try
        Loop

    End Sub
    Private Function GenerateString(ByVal length As Integer, ByVal content As Integer, ByVal casing As Integer) As String
        Dim r, r1, r2 As New Random
        Dim gString As String = String.Empty

        Dim lowAlph As String = "abcdefghijklmnopqrstuvwxyz"
        Dim uppAlph As String = lowAlph.ToUpper

        Dim addLetter As Char

        Do Until gString.Length = length
            Select Case casing
                Case 0
                    Select Case r.Next(0, 2)
                        Case 0
                            addLetter = lowAlph.Substring(r.Next(0, 25), 1)
                        Case 1
                            addLetter = uppAlph.Substring(r1.Next(0, 25), 1)
                    End Select

                Case 1
                    addLetter = uppAlph.Substring(r1.Next(0, 25), 1)

                Case 2
                    addLetter = lowAlph.Substring(r.Next(0, 25), 1)
            End Select
            Select Case content
                Case 0
                    Select Case r.Next(0, 2)
                        Case 0
                            gString &= addLetter
                        Case 1
                            gString &= r1.Next(0, 9)
                    End Select
                Case 1
                    gString &= r1.Next(0, 9)
                Case 2
                    gString &= addLetter
            End Select
        Loop
        Return gString
    End Function