A U.S. court has ruled that the FBI can hack into a computer without a warrant—a move which is troubling privacy advocates.

The criminal case involves a child pornography site, Playpen, that had been accessible through Tor, a browser designed for anonymous web surfing.

The FBI, however, managed to take over the site in 2014, and then tracked down and arrested its members by hacking their computers. This allowed law enforcement to secretly collect their IP addresses.

One of the arrested suspects has argued that the evidence against him had been unlawfully seized. But a U.S. court in Virginia has ruled in favor of the FBI, according to court documents unsealed on Thursday.

The judge, Henry Morgan, ruled that even though the FBI obtained a warrant to hack into the suspect’s computer, none was needed.

The suspect may have used Tor to keep his browsing anonymous, but his IP address still isn’t private information, the judge wrote in his ruling. This is because the IP address is given out to third parties in order to access the Internet and even the Tor network.

Privacy advocacy group, Electronic Frontier Foundation, is opposed to this part of the ruling.

“The implications for the decision, if upheld, are staggering,” wrote Mark Rumold, an attorney with the group in a blog post. Law enforcement could seize information from a person’s computer without a warrant, probable cause or any suspicion at all, he said.

“To say the least, the decision is bad news for privacy,” he added.

Morgan, however, said in his ruling that the rise of hacking has changed expectations about privacy.

“For example, hacking is much more prevalent now than it was even nine years ago,” he said. “Now, it seems unreasonable to think that a computer connected to the Web is immune from invasion.”

As a result, Tor users “cannot reasonably expect” to be safe from hackers, he added. The FBI also didn’t violate the Fourth Amendment of the U.S. Constitution by hacking into the suspect’s computer. Law enforcement should be able to use cutting-edge technology to stop crimes done in secrecy, Morgan said.

Rumold, however, expects that this part of judge’s ruling probably won’t hold up in appeal.