A coalition of global law enforcement agencies have sent emails to more than 75,000 alleged cybercriminals who paid for a service to launch cyberattacks that can knock websites offline.

On Thursday, Europol announced the coordinated operation against several distributed denial-of-service (DDoS) for-hire services, which allow criminals to launch cyberattacks without needing any hacking skills or running their own infrastructure. Part of the law enforcement action — dubbed Operation PowerOFF — included Europol sending warning emails and letters to more than 75,000 people who are suspected of using these DDoS-for-hire services.

Europol said it obtained information about the alleged cybercriminals by raiding and seizing servers associated with these services, allowing the police to identify their registered users. The action also resulted in four arrests, the takedown of 53 domains, and police executing 24 search warrants.

DDoS attacks remain relatively common for their ability to cause disruption while being relatively easy to carry out, thanks in part to for-hire services. Last year, Cloudflare said it mitigated what it called the largest DDoS attack to date, which registered a peak of 29.7 terabits per second.

In the last few years, the FBI has conducted several operations against DDoS-for-hire services.