Senior officials from the United States and United Kingdom on Monday said Russian government-backed hackers have infected computer routers around the world in coordinated cyberattacks aimed at the theft of intellectual property and cyber espionage.

The targets were critical infrastructure, government agencies and businesses, according to the officials, who also alluded to the possibility of retaliatory measures.

“When we see malicious cyber activity, whether it be from the Kremlin or other malicious nation state actors, we are going to push back,” said Rob Joyce, the White House cybersecurity coordinator.

The senior officials revealed to reporters during a conference call their intent to issue a joint alert regarding the attacks, because the infected routers could be used to launch future offensive cyber operations.

“They could be pre-positioning for use in times of tension,” said Ciaran Martin, chief executive of the British government’s National Cyber Security Centre cyber defense agency, who added that “millions of machines” were targeted in the campaign.