As many as 100 vehicles offered through the Car2Go rental app were stolen across Chicago and police have arrested at least 16 people in relation to the thefts.

The Chicago Police Department told Motherboard that most of the vehicles have been recovered but said it was unsure if there were any others still missing.

Car2Go was founded by Daimler and operates in cities around the world, including in Chicago, and allows users to rent Mercedes-Benz and Smart vehicles. The vehicles can be unlocked through a mobile application but Car2Go says the vehicles were not stolen due to a “hack” but says it is a “fraud issue” without providing additional details.

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In a statement, the Chicago Police Department said most of the vehicles had been recovered in Chicago’s West Side.

“We were alerted by a car rental company that some of their vehicles may have been rented by deceptive or fraudulent means through a mobile app. Due to the information provided by the company, numerous vehicles have been recovered and persons of interest are being questioned. We are working with the company to determine whether there are any other vehicles whose locations cannot be accounted for. At this time, the recoveries appear to be isolated to the West Side. The investigation is ongoing,” authorities said.

Taking to Twitter, Car2Go announced that it will temporarily pause its service in Chicago as the investigation continues. The company says that “no personal or confidential member information has been compromised.”

“Clarification: We were not hacked. This is an instance of fraud, isolated to Chicago, and we are currently working with law enforcement,” Car2Go added.