Ad tech company Gravity4 has made a 564,700,000 kr ($67.4 million) bid to acquire publicly traded rival Swedish company TradeDoubler. The news is startling for a number of reasons: It comes exactly a week after another publicly traded ad tech company, Rocket Fuel, rejected a $350 million takeover bid from Gravity4 saying it was "not credible." At the time Gravity4 originally made its unsolicited offer, Rocket Fuel's stock surged 18% in the pre-market and briefly stopped trading.