IRS has now set foot to control tax cheats using Bitcoin. IRS has stated that because of Bitcoins being anonymous, it makes it tough to find out who had made the transaction just by knowing their Bitcoin addresses.
Although still, Bitcoins are pseudonymous. Hence, sites such as coinbase can intelligently find out who eventually had made the transaction by having a look at the various sources where their customers spend Bitcoin on and their time records and of course with some help from Artificial Intelligence too.
Using this, they're also sure that this can prove to be significant in keeping eye over illegal drug supplies and other such activities.