Private equity firm Sterling Partners has sold SecureNet Payment Systems to Worldpay. Terms were not disclosed. Sterling purchased SecureNet in 2012. Worldpay has been owned by private equity firms Bain Capital and Advent International since 2010. Worldpay and SecureNet are payment processors of merchant card transactions. Headquartered in London, Worldpay operates in 31 countries. It ranks 3rd among all merchant acquirers worldwide and is Europe’s largest. Worldpay processes 26 million transactions a day in 120 currencies from more than 600,000 merchants. Last year it handled more than $...