The man was detained Monday in Kyiv following a long-running investigation led by French authorities with support from Ukrainian police.
Europol said the suspect ran xss.is, a major Russian-speaking platform with over 50,000 users that enabled trading of stolen data, hacking tools and illicit services. He also operated a secure messaging service for criminals and acted as an intermediary for transactions. Investigators say he has been active in cybercrime for nearly 20 years.