A new era in cyber warfare has arrived.

In charging five Chinese military officials with cyber espionage, the U.S. extended the battle lines to combatants who wage war behind keyboards.

Already at odds with China over the communist country's air defense zone, trade pacts and human rights, the U.S. slapped China in a manner often threatened but never before used.

The indictments showcase growing frustration with Chinese cyber theft that is draining hundreds of billions of dollars from the American economy each year, analysts said. And it signaled a newly aggressive approach in combating cyber attacks that are becoming easier to carry out.

“The espionage problem is growing and can only be controlled if there is a response,” said James Andrew Lewis, a senior fellow and director of the Strategic Technologies Program at the Center for Strategic and International Studies.

“There are rules in espionage, implicit and unstated, but understood,” he added. “One rule is to not overdo it. [Edward] Snowden's leaks showed that the U.S. ignored this rule to its cost. Now China has been called out as well.”

At least 3,000 U.S. companies were the victims of cyber hacking last year, according to the FBI, with China seen as the leading perpetrator.

The Chinese military officials infiltrated the U.S. businesses' computer networks with relative ease, relying on deceptive email attachments and web links to get U.S. workers to turn over secrets about their companies — techniques that are commonplace to most people who have spent time behind a computer.

“Once you get out of Washington, folks often think of cybersecurity as somebody else's problem -- but your cyber systems, your intellectual property is at risk,” said Dean Cheng, a senior research fellow at the Heritage Foundation's Asian Studies Center. “Hopefully, this gets people out of that complacent way of thinking."

The White House argues that spying purely for economic benefit is indefensible as opposed to cyber espionage for national security reasons. In Beijing, however, those are synonymous. It would effectively take China years to develop the types of technologies and products already in use in the U.S., and the Asian nation sees cyber spying as a shortcut to close that gap.

In announcing the charges, Attorney General Eric Holder said Westinghouse, Alcoa, U.S. Steel Corp., the United Steel Workers Union, Allegheny Technologies and SolarWorld were targeted for “no other reason than to advantage state-owned companies and other business interests in China.”

Many of those companies develop products critical to the U.S. armed forces, giving China's military the motivation to scoop up American secrets.

The Chinese officials likely will never stand trial in the U.S., but the charges carried immediate diplomatic consequences.

Some analysts now fear that American companies doing business in China will become even bigger targets. And the Chinese government has raised the possibility of leveling charges against Americans -- potentially even military officials -- they say are guilty of the same tactics being condemned by the Justice Department.

Tensions are unlikely to ease anytime soon. In addition to cyber hacking, Washington and Beijing have traded jabs over Chinese actions in the East China Sea and over stalled trade deals.

That the Obama administration chose to pick another fight with the rising superpower, experts said, demonstrates the tremendous risk of letting China’s actions go unchecked.

“Whether it is yet another straw or a brick is unclear,” Heritage's Cheng said of the charges, “but it’s another part of this deteriorating relationship where both sides are looking at each other with increasing suspicion.”