Two of Uber's executives have been arrested in France over allegations they are running an "illegal taxi service".The company's CEO for France, Thibaud Simphal and its General Manager for Europe Pierre-Dimitri Gore-Coty were taken into custody and questioned about what the authorities are calling "illicit activity".It's also reported that Police think Uber are "concealing digital documents".The pair are reported to have been bailed to appear in court at the end of September.Uber is unpopular with taxi drivers in most countries because it's felt the business's app-based service is undermining the regulated taxi market.Last week there were violent protests by taxi drivers in France against it.