The FBI warned on Friday that foreign cybercriminals had compromised "hundreds of thousands" of home and small-office router devices around the world which direct traffic on the internet by forwarding data packets between computer networks.
In a public service announcement, the FBI has discovered that the foreign cybercriminals used a VPNFilter malware that can collect peoples' information, exploit their devices and block network traffic.
The announcement did not provide any details about where the criminals might be based, or what their motivations could be.
"The size and scope of the infrastructure by VPNFilter malware is significant," the FBI said, adding that it is capable of rendering people's routers "inoperable."
It said the malware is hard to detect, due to encryption and other tactics.
The FBI urged people to reboot their devices to temporarily disrupt the malware and help identify infected devices.
People should also consider disabling remote management settings, changing passwords to replace them with more secure ones, and upgrading to the latest firmware.