The U.S. Internal Revenue Service (IRS) has put bitcoin anonymous users under the microscope as they hunt down possible tax evaders.

According to the New York Times, the US IRS has directed Coinbase, the largest Bitcoin exchange in the United States, to turn over the identity and full transaction history of millions of customers who bought virtual currency from the company from 2013 to 2015.

Under the rules set by regulators, companies engaged in the buy and sell Bitcoins are required to record the identities of people who buy and sell virtual currency on their platforms.

Coinbase, a start-up based in San Francisco with funding from several leading venture capital firms, was put under intense scrutiny after tax agents uncovered found three cases in which people were using Bitcoin to evade taxes.