Payments vendor VeriFone has stepped up its assault on Square, using Facebook ads to bash its rival's security measures and encourage users to switch.
VeriFone caused a storm earlier this month when its CEO Douglas Bergeron posted an open letter and video slamming Square, accusing it of "serious security flaws" that put "consumers in dire risk".
His firm even built an application to show how Jack Dorsey's Square could be turned into a skimming device.
Now, VeriFone has introduced a sponsored ad on Facebook declaring: "Be Secure. Not Square. Trade in your Square credit card reader for a free, SECURE device from VeriFone. Free trade-in offer!"
The add was spotted by by LikeDeal founder Raul Alvarez who tweeted a picture to FourSquare business developer Tristan Walker along with the message: "Wow @tristanwalker VeriFone is playing nasty with Facebook ads!"