An improved technique authenticates a user based on an ability to corroborate previous transaction data sent by a user device. Along these lines, the improved technique makes use of an independent information source for verifying the accuracy of previous transaction data obtained by a given collector. For example, when a collector of location data is a GPS unit of a cell phone, an independent information source may be a cell tower closest to the cell phone at the time of the transaction. While location data provided by the cell tower may not be as precise as that provided by the GPS unit, such data is useful for corroborating the location data from the GPS unit. In this scenario, if the data provided by the cell tower fails to corroborate that provided by the GPS unit, then the GPS unit adds significant risk to authenticating the user.