As devices’ price tags rise and customers use them for longer periods before trading up, the secondhand mobile device market is flourishing. That presents an opportunity for device manufacturers to expand their installed base and for carriers to offer lower-priced device options to attract or retain customers — but it also raises issues around the security of the personal information on devices.

According to recent research from B-Stock, which is a business-to-business marketplace for trade-in and overstock mobile devices, the used phone market is worth about $25 billion now and is “growing faster than the primary market.”