Britain and the United States on Monday released a rare joint statement warning of "malicious cyber activity" carried out by the Russian state.
The technical alert was issued by the UK's National Cyber Security Centre, the US Federal Bureau of Investigation and Department of Homeland Security.
"The targets of this malicious cyber activity are primarily government and private-sector organisations, critical infrastructure providers and the Internet Service Providers (ISPs) supporting these sectors," the statement said.
It warned everyone from internet service providers to home office customers to heed the warning, after the government agencies found cyber attacks targetting devices such as internet routers.
"Russian state-sponsored actors are using compromised routers to conduct spoofing 'man-in-the-middle' attacks to support espionage, extract intellectual property, maintain persistent access to victim networks and potentially lay a foundation for future offensive operations," the UK and US warned.
They cited cyber security research organisations and other governments as providing evidence of such attacks, without providing details of their timing or scale.
"The current state of US and UK network devices, coupled with a Russian government campaign to exploit these devices, threatens our respective safety, security, and economic well-being," the technical alert said.
The joint statement comes amid worsening relations between the two countries and Moscow, after Washington and London launched coordinated strikes against Russia's ally Syria.
Britain and the US have also blamed Russia for the poisoning of a former double agent in the UK, prompting a global diplomatic crisis.