WASHINGTON (Reuters) - Wisconsin, Ohio, California and 10 other states said on Friday they were among 21 states that Russian government hackers targeted in an effort to sway the 2016 presidential election in favor of Donald Trump though no votes were changed.

The Department of Homeland Security confirmed it had notified the states of the activity but declined to identify them. Russia has denied election meddling, and President Trump has denied any collusion with Russia.

Alabama, Alaska, Colorado, Connecticut, Florida, Minnesota, Texas and Washington state also confirmed they were targeted by Russian hackers but said they were not successful. Arizona and Illinois confirmed last year that they were targets.

The Associated Press confirmed Iowa, Maryland, North Dakota, Pennsylvania, Delaware, Oregon, Oklahoma and Virginia were also targets, bringing the total states identified to 21. Those states did not immediately return messages seeking comment late Friday.

“There remains no evidence that the Russians altered one vote or changed one registration,” said Judd Choate, president of the U.S. National Association of State Election Directors.

Wisconsin Elections Commission Administrator Michael Haas said Homeland Security told the states that “Russian government cyber actors” targeted state voter registration systems.

Homeland Security officials have said that in most of the 21 states only preliminary activity was observed from hackers and a small number of networks were compromised. Some states had complained in June they had no idea if Russians had attempted to infiltrate their systems.

California Secretary of State Alex Padilla said Friday that hackers had scanned state election systems but not breached the system. “It is completely unacceptable that it has taken DHS over a year to inform our office of Russian scanning of our systems, despite our repeated requests for information,” he said.

Homeland Security spokesman Scott McConnell said in a statement the government believes “officials should be kept informed about cybersecurity risks to election infrastructure” but also wants to protect “the integrity of investigations and the confidentiality of system owners.”

U.S. intelligence agencies have concluded the Kremlin orchestrated an operation that included hacking and online propaganda intended to help Trump win, Reuters reported in August.

Senator Mark Warner, a Virginia Democrat who co-chairs the Senate Cybersecurity Caucus, said Friday in a statement it is “unacceptable that it took almost a year after the election to notify states that their elections systems were targeted.”

He said officials must inform states of attempts to enter election systems “just as any homeowner would expect the alarm company to inform them of all break-in attempts, even if the burglar doesn’t actually get inside the house.”

Colorado Secretary of State Wayne Williams said DHS told it that its systems were scanned in the weeks before the 2016 election. “A scan is similar to burglars jiggling the doors of a house and moving on when they realize the doors are locked,” the state said.

Washington state’s top election official, Kim Wyman, said the state learned in 2016 of attempted intrusions from Russian internet addresses and immediately alerted the Federal Bureau of Investigation.

The list of targets includes battleground states like Wisconsin, Ohio and Iowa, but other key states like Michigan said Friday they were told they were not targeted. It also included states that were not seriously contested like California and Texas.

Wisconsin was one of a handful of battleground Midwestern states that helped Trump win the presidency over Democratic rival Hillary Clinton. Trump carried the state by 22,748 votes, or about 0.8 of a percentage point. Many of the other states were not seriously in contention in the 2016 race.

Several congressional committees are investigating and special counsel Robert Mueller is leading a separate probe into the Russia matter, including whether Moscow colluded with the Trump campaign.