The Pentagon plans to add more than 4,000 people to its efforts to combat the growing number of cyberattacks in the country and to take the offensive against attacks from foreign countries.

Increasing the Defense Department’s Cyber Command by more than 4,000, well above today’s level of 900, will be a challenge, a New York Times article quoted defense officials as saying. The department said officials know that recruiting, training and retaining that many qualified people will be a difficult chore.

But, as William J. Lynn III, a former deputy defense secretary, said, “The threat is real and we need to react to it.”

The Pentagon is planning three different operations under the Cyber Command umbrella: forces that protect the computer systems of the electric grid and infrastructure, another that develops and conducts offensive attacks on adversaries considered threats and a force dedicated to protecting the Pentagon’s own computer systems.

The Times article said the expansion of the Cyber Command was part of a strategy by Department of Defense Secretary Leon Panetta, who warned in October that a “cyber-Pearl Harbor” was a possibility and that the U.S. was becoming more vulnerable to foreign attacks that could take down the electric grid, transportation infrastructure, financial system and government.

Specifically, defense officials said they were becoming more convinced that a summer computer attack on oil company Saudi Aramco came from Iran, adding that the U.S. was already engaged in attacks and counterattacks with the Middle Eastern country. They also believe that China and Russia, which are much more capable than Iran, have been responsible for cyberattacks on U.S. companies and government agencies.

To underscore how important the Pentagon considers cybersecurity, the article noted that the massive growth in Cyber Command will happen as it is cutting budgets elsewhere, including conventional armed forces.