Russian hackers may be coming for you, and there’s one way to stop them: Turn off your Wi-Fi.

The Federal Bureau of Investigation said Friday anyone with a small office or home router should reboot it to stop the spread of malware. A potential attack had infected hundreds of thousands devices across 54 countries with software called VPNFilter, which was traced back to Ukraine where it was first found in 2016, it said.

The software had not had any negative effects yet, but would allow devices to be hacked for a number of nefarious purposes. Ukranian officials said in a statement they suspect Russia is behind the attack.

To thwart it, the FBI has instructed Americans to do what many IT professionals ask you to do when you have a problem with your Wi-Fi: Turn off your router and then turn it back on again.

“The FBI recommends any owner of small office and home office routers reboot the devices to temporarily disrupt the malware and aid the potential identification of infected devices,” it said in a statement.

While the hack does not affect all routers, experts suggest everyone upgrade their home and office internet security, install the latest firmware and change the default password, said Chester Wisniewski, principal research scientist at security firm Sophos.

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The FBI said last week it had seized the domain used to issue instructions to the infected devices. When users reset their machines, the traffic will reroute through the bureau’s site to clean them up.

This particular kind of vulnerability is alarming because it can be used for a number of attacks, said Caleb Barlow, vice president of threat intelligence at IBM IBM, -1.39% . It allows the machine to install additional software or internally change devices rendering them unusable.

“Think of it like a garage door — once you have access to it, you can drive anything from a bicycle to a bus into it,” he said. “It is up to the adversary to decide what to park in that garage.”

The hack underscores ongoing issues with the security of routers, which rarely automatically update with patches for vulnerabilities. Experts suggest not using routers issued by your internet service provider and instead buying more expensive, and more secure devices.

“This should be the default moving forward,” said David Ginsburg, vice president at Cavirin, a Santa Clara, Calif.-based provider of cybersecurity. “We’re used to this with our smartphones and laptops, and think nothing of updates.”