(CNN)-- Cyber hackers -- possibly working for foreign governments -- are trying to infiltrate the Democratic and Republican presidential campaigns, a senior U.S. intelligence official said Wednesday.
"We've already had some indications of that," James Clapper, the director of national intelligence, said in Washington.
During the 2008 presidential campaign, U.S. intelligence agencies traced massive cyber attacks to China. At that time, both the Democratic candidate, now-President Barack Obama, and his Republican rival John McCain, were targeted. Officials said hackers were trying to seize sensitive data, including private emails and information on high-level economic and national security briefings senior aides might have received.
The Department of Homeland Security and the Federal Bureau of Investigation "are doing what they can do educate both campaigns against potential cyber threats," Clapper said at an event at the Bipartisan Policy Center.
He didn't offer any detail on how the intrusions were detected or name which campaigns were targeted. But he offered a prediction.
"As the campaigns intensify, we'll probably have more," Clapper said.
Clapper was addressing the challenge of balancing the need to protect U.S. businesses and citizens' privacy in the face of an "incredibly complex set of cyber threats."
Those threats come from a dizzying array of enemies, he said, from groups like Anonymous to nation states like Iran, which has attacked U.S. banks and infiltrated the control system of a dam in New York.
North Korea's attack on Sony Pictures damaged a major U.S. corporation, while China is the suspected culprit behind the 2015 theft of millions of federal workers' security-related personal information in an attack on the Office of Personnel Management.
"The Russians and Chinese who are far more sophisticated and could do real damage if so inclined. Then there are terrorist groups," Clapper said. "Each has different objectives. The one thing they have in common, they all operate on the same internet."
Clapper said in his decades-long career in intelligence, he doesn't "recall a time when we've been beset by a wider array and more diverse array of threats and crises than we are today." He puts cyber at the top of the list when he discusses risks because of the variety of intrusions that come "around the clock."
That, he said, "will likely expand" at increasing costs to U.S. businesses and economic security.