Europol said Tuesday that it has arrested a “main target” and detained another suspect from an online extortion group that threatened to boot companies offline if they didn’t pay up.

The group is known as DD4BC, which stands for Distributed Denial of Service for Bitcoin, after the cyberattack of that name, which knocks websites offline by overwhelming them with a flood of traffic. The attackers sent ransom notes with their threats, requesting varying sums in bitcoin.