FILE - A photo illustration shows hands typing on a computer keyboard in Los Angeles.
FILE - A photo illustration shows hands typing on a computer keyboard in Los Angeles.

The U.S. government's top intelligence official says he's seen indications of foreign hackers attempting to spy on the U.S. presidential candidates.

"We've already had some indications," said Director of National Intelligence James Clapper, who added "as the campaigns intensify, we'll probably see more of it."

Clapper, whose remarks came Wednesday at a cybersecurity event in Washington, said FBI and Homeland Security Department officials are working with the presidential campaigns to counter any cyberthreats.

The apparent cyber intrusions follow a pattern that was established during the last two presidential elections. U.S. intelligence officials say hacking was rampant in 2008 and, four years later, President Barack Obama and his Republican opponent Mitt Romney were targets of Chinese hackers.

The worldwide hacker group "Anonymous" and others have threatened "total war" against Republican candidate Donald Trump's campaign. Trump's campaign and business websites have already been defaced and spammed at least six times, one of which resulted in the release of his Social Security number.

Clapper said cyberthreats come from a wide variety of sources, including countries. "The Russians and Chinese are far more sophisticated and could do real damage if so inclined. Then there are terrorist groups. Each has different objectives," he said.

China is suspected of stealing millions of U.S. federal workers' personal information in a 2015 attack on the Office of Personnel Management.

To combat the intrustions, Clapper recommends that Internet users patch their software frequently and categorize information to limit its access to hackers.

VOA National Security correspondent Jeff Seldin contributed to this report.