Britain is significantly increasing its ability to wage war in cyberspace with the creation of a new offensive cyber force of up to 2,000 personnel.
The plan by the Ministry of Defence and GCHQ comes amid a growing cyber threat from Russia and after the UK used cyber weapons for the first time to fight Islamic State.
The new force - expected to be announced soon - would represent a near four-fold increase in manpower focused on offensive cyber operations.
Made up of GCHQ officials, military personnel and contractors, it looks set to receive more than £250m in funding, according to one source.
A second source said that the figure would likely be higher.
General Sir Richard Barrons, a former commander of Joint Forces Command, which is responsible for military cyber, said enhancing the UK's ability to launch cyber attacks is paramount at a time when countries such as Russia are already on the offensive.
"By adopting offensive cyber techniques in the UK we are levelling the playing field and providing new means of both deterring and punishing states that wish to do us harm," he said.
The US-led campaign against IS in Iraq and Syria demonstrates the growing importance of cyber warfare in modern-day conflict.
Interviews with several former and serving security and military officers reveal:
- David Cameron, as prime minister, instructed his spy agencies and the armed forces at the start of 2016 to go after the IS media machine behind a series of gruesome online beheading videos of hostages, slick online magazines and a huge volume of other propaganda used to draw new recruits and incite violence.
- Britain, the United States and allies launched a series of secret cyber operations, including one called Glowing Symphony. They used malware to block access to data, placed fake stories to create confusion and deleted large volumes of material. IS financing was also targeted.
- GCHQ worked with special forces to deploy cyber attacks from laptops and handheld devices against IS commanders in Iraq and Syria to jam their ability to communicate electronically and to spoof them into running into real-world traps by feeding false instructions over the internet. "It was very effective," a source said.
Details of the UK's ongoing cyber mission against IS - conducted in close coordination with the United States, Australia and other members of the "five eyes" intelligence community - are highly classified.
In a rare public acknowledgement, Jeremy Fleming, the director of GCHQ, spoke about the impact his agency and the MoD were having against the terrorist group earlier this year.
"These operations have made a significant contribution to coalition efforts to suppress Daesh [IS] propaganda, hindered their ability to co-ordinate attacks, and protected coalition forces on the battlefield," Mr Fleming said.
The United States has avowed its part in the Glowing Symphony offensive from November 2016 into early 2017 - an operation that Britain played an equal but until today unacknowledged role in.
This was only one element of a much wider online offensive.
"It was a small example of the kind of destructive things you can do to disrupt, and stop them distributing propaganda material," one security source said.
The mission has reduced the volume and quality of IS propaganda on the internet.
Analysts point to the disappearance of an online magazine, originally called Dabiq and then renamed Rumiyah, that was produced by IS every month.
The quality of the content eroded from 2016, according to Charlie Winter, a senior research fellow at the International Centre for the Study of Radicalisation and Political Violence.
Spoof versions of the magazine also emerged in what might have been part of the cyber offensive. A final version of Rumiyah was published a year ago.
The UK-end of the cyber mission against IS is run out of GCHQ's headquarters in Cheltenham and the military's permanent joint headquarters in Northwood.
The new joint cyber force will be established at a separate location that has yet to be agreed upon. Another detail still to be hammered out is selecting who will run it.
One suggestion is for the military and GCHQ to take it in turns, with one organisation fielding the chief and the other fielding the deputy for one term and then switching.
The online campaign against IS is one element in a much broader, covert offensive that was just as important at dismantling the so-called caliphate in Iraq and Syria as the bombs and bullets, according to military and security officials who were involved.
This included disrupting IS funding and logistics to make it harder for the group to pay its fighters and supply them with weapons, ammunition, food and other supplies.
Industry: Cyber Security news