Md5 hash entire listbox - vb.net

Question

As of now I can hash listbox selected item with
Public Function Md5FromString(ByVal Source As String) As String
Dim Bytes() As Byte
Dim sb As New StringBuilder()
'Check for empty string.
If String.IsNullOrEmpty(Source) Then
Throw New ArgumentNullException
End If
'Get bytes from string.
Bytes = Encoding.Default.GetBytes(Source)
'Get md5 hash
Bytes = MD5.Create().ComputeHash(Bytes)
'Loop though the byte array and convert each byte to hex.
For x As Integer = 0 To Bytes.Length - 1
sb.Append(Bytes(x).ToString("x2"))
On Error Resume Next
Next
'Return md5 hash.
Return sb.ToString()
End Function
And collect them in another listbox, but I get an error (An unhandled exception of type 'System.StackOverflowException' occurred in System.Windows.Forms.dll) after about 4K somewhere random as if it fails to update a label or textbox then have to edit my list and reset and i just feel there is a better way to do this.
Can someone more experienced offer some guidance in making this routine more efficient?

Answer 1

Not sure where your error is coming from, but you definitely don't need to be using Create() in a tight loop. Store it as a local variable and re-use it by declaring it as static (or keep the reference at class level instead):
Public Function Md5FromString(ByVal Source As String) As String
Static local_MD5 As MD5 = MD5.Create
If String.IsNullOrEmpty(Source) Then
Throw New ArgumentNullException
End If
Dim sb As New StringBuilder()
For Each b As Byte In local_MD5.ComputeHash(Encoding.Default.GetBytes(Source))
sb.Append(b.ToString("x2"))
Next
Return sb.ToString()
End Function

Answer 2

Ok, here is how I figured out to work better than what I was doing by a tremendous bound, I was waiting for about an hour for 4K hashes now I get 50K in mins by hashing the string as they come in from the .txt. May still be messy but it works way faster.
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
TextBox1.Text = ""
OpenFileDialog1.Title = "Please Select a File"
OpenFileDialog1.InitialDirectory = "C:temp"
OpenFileDialog1.ShowDialog()
Dim path As String = OpenFileDialog1.FileName
TextBox1.Text = path
Dim lines() As String = IO.File.ReadAllLines(TextBox1.Text)
For Each line In lines
ListBox1.Items.Add(Md5FromString(line) + ":" + line)
ListBox1.Refresh()
Label1.Text = ListBox1.Items.Count
Label1.Refresh()
If ListBox1.Items.Count = 1000 Then
save()
ListBox1.Items.Clear()
ListBox1.Refresh()
Label1.Text = 0
End If
Next
' ListBox1.SelectedIndex = 0
End Sub