def readProtocolVersion(self, data):
        """
        Read protocol version
        @param data: Stream may contain protocol version string (ProtocolVersion)
        """
        data.readType(self._version)
        if not self._version.value in [ProtocolVersion.RFB003003, ProtocolVersion.RFB003007, ProtocolVersion.RFB003008]:
            self._version.value = ProtocolVersion.UNKNOWN