American intelligence officials say Russia compromised U.S. election systems in seven states, according to a new report.

NBC reports Russian hackers breached state websites or voter registration databases in Alaska, Arizona, California, Florida, Illinois, Texas and Wisconsin ahead of the 2016 elections. Federal intelligence officials never told the states, though some were informed that a foreign entity attempted to probe their systems but didn't disclose it was Russia.

Sources told NBC that not all information was shared due to the classification of sensitive information involving spies eavesdropping on Russian communications.

A spokesman for the Department of Homeland Security (DHS) told Reuters that the report was "factually inaccurate and misleading" in a statement.

It's unclear how much was compromised, but all state and federal officials who spoke with NBC said that "no votes were changed and no voters were taken off the rolls."

U.S. intelligence agencies agreed in 2016 that Russia intentionally attempted to interfere with the presidential election to help Republican candidate Donald Trump defeat Democrat Hillary Clinton. Thirteen Russians and three Russian entities were charged by Special Counsel Robert Mueller earlier this month and accused of using bogus social media postings and advertisements fraudulently purchased in the name of Americans to sway political opinion during the race.

According to NBC, the DHS told 21 states in September that they had been targeted, and officials acknowledged that some of those attempts were successful.

NBC reports six of the seven breached states still deny they were breached based on their own cyber investigations, suggesting a high level of sophistication in the Russian attack and a lack of preparation for U.S. states to protect themselves in the 2018 midterm elections. Only Illinois election officials have confirmed a breach, allowing foreign hackers to access 90,000 voter registration records.

According to Vox, Sam Liles, the then-acting director of the Cyber Division of the DHS, testified that Russians were likely testing American election systems' vulnerability for a possible larger attack in the future.

Adm. Mike Rogers, head of U.S. Cyber Command and the National Security Agency (NSA), reportedly told lawmakers on Tuesday that America is "taking steps, but we're probably not doing enough" to stop more Russian interference: "They haven't paid a price at least that's sufficient to get them to change their behavior."