The U.S. government believes hackers from Russia or elsewhere may try to undermine next week's presidential election and is mounting an unprecedented effort to counter their meddling, American officials told NBC News.
The effort is being coordinated by the White House and the Department of Homeland Security, but reaches across the government to include the CIA, the National Security Agency and other elements of the Defense Department, current and former officials say.
Russia has been warned that any effort to manipulate the actual voting or vote counting would be viewed as a serious breach, intelligence officials say.
"The Russians are in an offensive mode and [the U.S. is] working on strategies to respond to that, and at the highest levels," said Michael McFaul, the U.S. ambassador to Russia from 2012 to 2014.
Officials are alert for any attempts to create Election Day chaos, and say steps are being taken to prepare for worst-case scenarios, including a cyber-attack that shuts down part of the power grid or the internet.