Some employees of a credit card company got in trouble for this sort of thing a while ago. They were running queries against customer transactions to figure out

Some employees of a credit card company got in trouble for this sort of thing a while ago. They were running queries against customer transactions to figure out sales ahead of earnings calls. For example, they figured out that Chipotle was going to beat expectations and bought a ton of stock just before the earnings call. (This very predictably got the attention of the SEC)