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There have been hacking attempts on election systems in more than 20 states — far more than had been previously acknowledged — a senior Department of Homeland Security official told NBC News on Thursday.

The "attempted intrusions" targeted online systems like registration databases, and not the actual voting or tabulation machines that will be used on Election Day and are not tied to the Internet.

The DHS official described much of the activity as “people poking at the systems to see if they are vulnerable.”

“We are absolutely concerned,” the DHS official said. “The concern is the ability to cause confusion and chaos."

Only two successful breaches have been disclosed, both of online voter registration databases, in Illinois and Arizona over the summer.

Related: NSA Chief: Potential Russian Hacking of U.S. Elections a Concern

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While those two hacks were linked to hackers in Russia, the DHS official did not say who was responsible for the other failed attempts, noting that "we're still doing a lot of forensics."

Meanwhile, intelligence officials tell NBC News there is now "no doubt" the Russian government is trying to influence the election.

Classified material, prepared for briefings of Donald Trump and Hillary Clinton and examined by NBC News, reveals that officials have drawn "direct links" between Vladimir Putin's government and the recent series of hacks and leaks.

The secret material confirms what lawmakers on the Senate and House Intelligence Committees said they had concluded last week, based on briefings they received.

"At the least, this effort is intended to sow doubt about the security of our election and may well be intended to influence the outcomes of the election — we can see no other rationale for the behavior of the Russians," Sen. Dianne Feinstein and Rep. Adam Schiff, both D-Calif., said in a statement.

Related: Russians Hacked Two U.S. Voter Databases, Officials Say

For weeks, American officials have been saying that Russian intelligence agencies were behind hacks into the DNC, state election databases and other political entities, but they weren’t definitive about the motive since nations routinely hack into their adversaries' political organizations to gather information for spying purposes.

In recent days, U.S. officials tell NBC News, American spy agencies have determined that the Russian government was behind the leaks of Democratic National Committee emails to Wikileaks and others — and that the goal was to undermine confidence in the American presidential election.

Another possible aim: sending a geopolitical warning.

NBC News has learned that this summer, Adm. Michael Rogers, director of the National Security Agency, told congressional intelligence committees that Washington believes "potential adversaries might be leaving cyber fingerprints on our critical infrastructure partly to convey a message that our homeland is at risk if tensions ever escalate toward military conflict."

Related: Could Russian Hackers Spoil Election Day?

FBI Director James Comey told a congressional hearing this week that he is taking the threat to election systems "extraordinarily seriously."

"We are urging the states just to make sure that their deadbolts are thrown and their locks are on and to get the best information they can from DHS just to make sure their systems are secure," he told the House Judiciary Committee.

DHS has been pushing states to undergo free cyber-hygiene scans and other assessments before the Nov. 8 vote. Yet, as Homeland Security Secretary Jeh Johnson told a congressional committee this week, just 18 have signed up for the free help. The results of those scans are not available yet.