But they are confident that no breach would affect the outcome of the election.
The briefing came as other US officials told CNN of concerns that Russia is waging an "information operation" to sow doubts about the US presidential election.
The DHS is in talks with all 50 states and have offered cyberhygiene scans to all of them, but not all have taken advantage of this help. DHS has also offered other risk and vulnerability scans that can be done both remotely and on the ground in any state.
They also have "fly away" teams, or incident response teams, ready to deploy wherever there could be a cybersecurity incident related to the election. Additionally, DHS will be monitoring for denial of service attacks from its National Cybersecurity and Communications Center on Election Day.
Concerns are mounting that next week's presidential election could be affected following breaches by hackers on election system databases in Illinois and Arizona earlier this year, and the US is also investigating probing of state voter registration systems, at least one of which they have sourced to Russia. But they have yet to see those systems tampered with.
This has been an ongoing issue, including what the US says is Russian state-sponsored hacking of the Democratic National Committee and other Democratic Party officials and organizations, as well as the release of documents hacked from a top Clinton campaign official and released via WikiLeaks in a manner consistent with Russian-sponsored operations.
The concerns as Election Day approaches include the release of more documents targeting campaigns, with the possible injection of faked documents; tampering with state voting registration systems; and organized trolling operations disseminating fake news -- for instance, of rigged counting.
Speaking to CNN's Jake Tapper on Friday, Rep. Adam Schiff, the ranking member on the House Select Committee on Intelligence, warned of interference in the election.
"They are capable of doing damage, they are capable of sowing further disarray," Schiff said. "Will they end up doing it? We don't know, and I think we are taking all the precautions that we can."