def escape_html(message):
    """Escapes HTML characters in the given message."""
    # Only the following characters need to be escaped
    # (https://wiki.ubuntu.com/NotificationDevelopmentGuidelines).
    message = message.replace('&', '&amp;')
    message = message.replace('<', '&lt;')
    message = message.replace('>', '&gt;')
    return message