The European Union’s top law enforcement agency has dealt a blow to an extortion ring targeting online gambling sites with distributed denial of service (DDOS) attacks.

In a statement published on its website, Europol announced that agents from Austria, Bosnia and Herzegovina, Germany and the UK cooperated on raids in December that netted two key members of the DD4BC (Distributed Denial of Service for Bitcoin) group, which directed its attacks primarily against the online gambling industry.

Europol’s Operation Pleiades focused on two members of the DD4BC ring located in Bosnia and Herzegovina, one of whom was identified as the “main target” of the raids. The UK Metropolitan Police Cyber Crime Unit was credited with identifying the location of the key suspects. Europol also said it had conducted multiple property searches and seized an “extensive” amount of evidence.

Europol claims that DD4BC has been responsible for several Bitcoin extortion campaigns since mid-2014. Gambling sites were the main targets but DD4BC recently branched out into targeting financial services and entertainment sector sites. The group also attempted to extort users of the infamous infidelity site Ashley Madison after a hack last year resulted in members’ email addresses being published online.