Military strategists believe cyberspace is the "fifth combat space" after land, sea, air and outer space.
Many developed countries expand great efforts to build cyber armies with advanced technologies and a substantial military budget as internet technology grows rapidly.
It has the largest cyber army and was the first country to build one. United States Cyber Command (USCYBERCOM) launched in May, 2010 with 4,900 employees hired in the following years.
USCYBERCOM announced it will introduce 40 cyber teams in March, 2013 as 13 of them are confirmed as attack forces to counterattack when the nation receives major cyber attacks.
The rest of the teams will support United States Pacific Command in Hawaii and Central Command in Florida.
The 40 teams have been established before the fall of 2015. Michael Rogers, commander of the US Cyber Command, said in Sept 2015 that the number of people in the cyber army will reach 6,200 before 2016.
The UK secretly built an army of hundreds of young hackers in 2001 with diverse backgrounds, some of whom committed minor network crimes.
The UK government established network security offices to coordinate security works in government and non-government departments.
The former Defense Secretary Philip Hammond announced they plan to hire hundreds of computer specialists as cyber reserves to work with the regular army to protect crucial data and networks in Sept, 2013.
UK Joint Forces Command requires the government to invest two billion pounds in five years and hire 300 hackers to be able to intrude into other countries' network when necessary.
Japan's Defense Ministry created a cyberspace defense force in 2011, intending to paralyze the enemies' combat system by controlling the network during combat.
It works on both offensive and defensive systems including building platforms for militia departments to share resources and recruiting 5,000 people to research and develop cyber products for network attacks.
Germany established its cyber army of information specialists in 2006.
The German Ministry of Defense claims its cyber army had combat ability on networks since the end of 2011. A spokesman of the Ministry of Defense said they will keep developing their cyber force.
India carries forward its independent research and development on network technology, encryption, chip technology and operating system.
India's high-speed network and navy encryption data communication network have increased India's military strength for cyber war in the future.
The Indian military clearly specified that they were to build a network system that can paralyse the enemy's conduct and control system and weapon system.
It also tries to extend the talent pool from society and the military to prepare for cyber combats.
South Korea came up with the blueprint of future information network development since 1999 and announced that it was establishing cyber command in Jan, 2010.
The nation has about 200,000 trained professionals. Five percent of annual national defense expenditure is used for R&D and improving core technologies for possible cyber war.
Israel has recruited talents who successfully hacked the US Department of Defense in 1998 and reinforced the research on cyber combat.
The country has a hands-on experience of cyber war.
It distorted web pages and attacked TV stations by cyber attacking to change public opinion regarding conflicts against Lebanon and Palestine.
It also tried to steal confidential information by intruding on military computers and blocked enemies' communication and command systems to win time for operations.