Just over a year ago, an independent hacker who goes by the handle P4x was himself hacked by North Korean spies. P4x was just one victim of a hacking campaign that targeted Western security researchers with the apparent aim of stealing their hacking tools and details about software vulnerabilities. He says he managed to prevent those hackers from swiping anything of value from him. But he nonetheless felt deeply unnerved by state-sponsored hackers targeting him personally—and by the lack of any visible response from the US government.

So after a year of letting his resentment simmer, P4x has taken matters into his own hands. “It felt like the right thing to do here. If they don’t see we have teeth, it’s just going to keep coming,” says the hacker. (P4x spoke to WIRED and shared screen recordings to verify his responsibility for the attacks but declined to use his real name for fear of prosecution or retaliation.) “I want them to understand that if you come at us, it means some of your infrastructure is going down for a while.”