An unprecedented joint statement between military and intelligence chiefs from the UK and US has highlighted transatlantic co-operation on cyber capabilities.
Leaders from GCHQ, the UK's joint forces command (JFC) and the US National Security Agency (NSA) discussed how to "counter and defend ourselves" against online threats.
It is the first time the JFC is understood to have participated in annual strategic talks between the GCHQ and NSA which is an indication of the increasing role cyber capability plays in the UK's defence.
The talks took place in the US and involved GCHQ director Jeremy Fleming, JFC commander General Sir Christopher Deverell, and US Admiral Mike Rogers, commander of US Cyber Command and director of the NSA.
They said: "Our organisations work extremely closely together to help keep the United States and United Kingdom safe.
"Our discussions focused on how best we deploy and develop our cyber capabilities to counter, and defend ourselves against, malign activity around the world.
"This co-operation has been part of our shared history for over 75 years, and will continue to be vital in protecting our countries.
"Every day our brilliant people share information and ideas as they counter shared threats in an increasingly digital world. We thank them for everything that they do."
Officials on both sides of the Atlantic are also concerned about Russian cyber attacks while North Korea has been blamed for the WannaCry attack which hit NHS hospitals.
An intelligence source said the talks in the US covered the "full range of topics" including "the work that we do together on hostile state activity".