VB.NET - vBulletin Login Module

Imports System.Text
Imports System.Net
Imports System.Security.Cryptography
Imports System.IO
Module vbloginsystem

    Public Function Login(ByVal Username As String, ByVal Password As String)

        Password = MD5(Password)
        Dim valid As Boolean = False
        Dim data As String = "vb_login_username=" & Username & "&vb_login_password=&s=&do=login&vb_login_md5password=" & Password & "&vb_login_md5password_utf=" & Password

        Try
            Dim request As HttpWebRequest = WebRequest.Create("http://yoursite.net/login.php?do=login")
            request.Method = WebRequestMethods.Http.Post
            request.ContentType = "application/x-www-form-urlencoded"
            request.UserAgent = "-- vBulletin Vaidation  --"



            request.ContentLength = data.Length

            Dim rStream As New StreamWriter(request.GetRequestStream)

            rStream.Write(data)
            rStream.Flush()
            rStream.Close()

            Dim response As HttpWebResponse = request.GetResponse
            Dim resReader As New StreamReader(response.GetResponseStream)

            Dim str As String = resReader.ReadToEnd


            If str.Contains("Thank you for logging in") Then
                valid = True
                MsgBox("Login Successful!", vbOKOnly + vbExclamation, "Message")
            Else
                MsgBox("Login Failed!, Please try again.", vbOKOnly + vbExclamation, "Message")
            End If


            response.Close()

        Catch ex As Exception
            MessageBox.Show(ex.Message, "Error login.php Login!", MessageBoxButtons.OK, MessageBoxIcon.Error)

        End Try

        Return valid

    End Function

    Public Function MD5(ByVal number As String) As String

        Dim ASCIIenc As New ASCIIEncoding
        Dim strReturn As String = String.Empty

        Dim ByteSourceText() As Byte = ASCIIenc.GetBytes(number)
        Dim Md5Hash As New MD5CryptoServiceProvider
        Dim ByteHash() As Byte = Md5Hash.ComputeHash(ByteSourceText)

        For Each b As Byte In ByteHash
            strReturn &= b.ToString("x2")
        Next

        Return strReturn

    End Function
End Module