There is no doubt that attacks of all kinds are on the rise. The Department of Homeland Security has been responding to intrusions on oil pipelines and electric power organizations at “an alarming rate,” according to an agency report last December. Some 198 attacks on the nation’s critical infrastructure systems were reported to the agency last year, a 52 percent increase from the number of attacks in 2011.

Researchers at McAfee, a security firm, discovered in 2011 that five multinational oil and gas companies had been attacked by Chinese hackers. The researchers suspected that the Chinese hacking campaign, which they called Night Dragon, had affected more than a dozen companies in the energy industry. More recently, the Department of Energy confirmed in January that its network had been infiltrated, though it has said little about what damage, if any, was done.

But security researchers say that the majority of those attacks were as ambiguous as the Telvent case. They appeared to be more about cyberespionage, intended to bolster the Chinese economy. If the goal was to blow up a pipeline or take down the United States power grid, the attacks would likely have been of a different nature.

In a recent report, Critical Intelligence, an Idaho Falls security company, said that several cyberattacks by “Chinese adversaries” against North American energy firms seemed intended to steal fracking technologies, reflecting fears by the Chinese government that the shale energy revolution will tip the global energy balance back in America’s favor. “These facts are likely a significant motivation behind the wave of sophisticated attacks affecting firms that operate in natural gas, as well as industries that rely on natural gas as an input, including petrochemicals and steelmaking,” the Critical Intelligence report said, adding that the attack on Telvent, and “numerous” North American pipeline operators may be related.

American intelligence experts believe that the primary reason China is deterred from conducting an attack on infrastructure in the United States is the simple economic fact that anything that hurts America’s financial markets or transportation systems would also have consequences for its own economy. It could interrupt exports to Walmart and threaten the value of China’s investments in the United States — which now include a new, big investment in oil and gas.

Iran, however, may be a different threat. While acknowledging that “China is stealing our intellectual property at a rate that qualifies as an epidemic,” Representative Mike Rogers, the Michigan Republican who chairs the House Intelligence Committee, added a caveat in an interview on Friday. “China is a rational actor,” he said. “Iran is not a rational actor.”

A new National Intelligence Estimate — a classified document that has not yet been published within the government, but copies of which are circulating for final comments — identifies Iran as one of the other actors besides China who would benefit from the ability to shut down parts of the American economy. Unlike the Chinese, the Iranians have no investments in the United States. As a senior American military official put it, “There’s nothing but upside for them to go after American infrastructure.”