Sky Bet, the most popular one in Britain, compiled extensive records about a user, tracking him in ways he never imagined.
The New York Times has a good story about What Sky Bet, The Gambling App, Knows About You. It talks about the profile that Sky Bet in the UK built on a customer who had an addiction problem with gambling.
The company, or one of the data providers it had hired to collect information about users, had access to banking records, mortgage details, location coordinates, and an intimate portrait of his habits wagering on slots and soccer matches.
We tend to focus on what the big guys have and forget all the lesser known information aggregators and middlemen who buy and sell data. This story also provides an example of how valuable data can be to a business like online gambling that wants to attract the clients who are likely to get addicted to gambling.