naughty rich text box

gistfile1.cs

private void SearchAndHighlightText()
  {
    ordersLogRichTextBox.SelectionLength = 0;
    string findStr = toolStripSearchTextBox.Text.Trim();
            
    int startIndex = 0;
    while (startIndex >= 0)
     {
                startIndex = ordersLogRichTextBox.Find(findStr, startIndex, RichTextBoxFinds.None);
                if (startIndex > 0)
                {
                    ordersLogRichTextBox.SelectionStart = startIndex;
                    ordersLogRichTextBox.SelectionLength = findStr.Length;
                    ordersLogRichTextBox.SelectionBackColor = Color.Yellow;
                    startIndex += findStr.Length;
                }
     } 
  }