Washington (CNN) Russian hackers are trying to gain access to the devices that control the flow of internet traffic, the US and UK warned Monday in an alert for organizations and individuals worldwide.

Though the governments are not sure how many devices have been compromised by the hackers nor what the objective is, the targeting affects millions of devices globally, US officials said on a call with reporters Monday morning.

"Once you own the router, you own the traffic traversing the router," chief Homeland Security cyber official Jeanette Manfra said, calling it a "fairly broad campaign" that is not targeting any sector in particular.

"It's a tremendous weapon in the hands of an adversary," echoed the FBI's Howard Marshall, the deputy assistant director of the cyber division.

The joint missive was the first time the US and UK governments have teamed up to put out such an alert. The warning says malicious Russian hackers have been targeting network infrastructure devices -- the types of devices that most internet traffic travels through, such as routers -- since 2015.

Read More