The Department of Homeland Security told officials in 21 other states on Friday that Russian hackers had tried to breach their election systemsbefore the November 2016 presidential election, but failed to change any votes.

For many states, the Friday calls were the first official confirmation of whether their states were on the list.

Department officials said hackers had only engaged in preliminary activity in most of the states and that in only a few electoral systems were compromised.

They declined to disclose which states had been notified to protect "the integrity of investigations and the confidentiality of system owners," according to department spokesman Scott McConnell. The notification was one year after Homeland Security first confirmed that hackers had targetted voting systems in US states.

Wisconsin Elections Commission Administrator Michael Haas had, however, said earlier that his state was one of those contacted by the department. He said officials told him that the Russian government had unsuccessfully tried to find vulnerabilities in in the state's networks to try to access voter registration databases.

Read more: US intelligence report: Putin 'ordered' targeted involvement in US election

Colorado Secretary of State Wayne Williams also said the department had told him Russian operatives had scanned the state's electoral system. "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.

Alabama, Minnesota, Connecticut, Ohio, and Washington State have also confirmed they had been attacked, but added that the hackers were unable to change any votes.

Arizona, California, Connecticut, Delaware, Florida, Illinois, Iowa, Maryland, Minnesota, North Dakota, Oklahoma, Oregon, Pennsylvania, Texas and Virginia were also contacted by Homeland Security, according to the Associated Press. The notification was reportedly the first time many had been informed of the attempts.

California's Secretary of State, Alex Padilla, criticized Homeland Security for not informing states sooner about the attacks.

"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," Padilla said in a statement. "The practice of withholding critical information from elections officials is a detriment to the security of our elections and our democracy."

Senator Mark Warner of Virginia, who sits on a congressional committee investigating Russian tampering in last year's election, welcomed the move by Homeland Security, but also criticized it for waiting so long to inform states. He said federal authorities needed to contact state and local governments as soon as they detected attacks against voting systems.

The notification comes in the midst of a high-profile investigation into possible collusion between the Russian government and now-President Donald Trump's campaign by special counsel Robert Mueller and other Senate congressional committees.

President Trump has said the story about Russian meddling in the 2016 election is a hoax, despite US intelligence agencies claiming in January that the Russian government had targeted Democratic Party nominee Hillary Clinton with hacks aimed at harming her presidential campaign.

amp/kl (AP, Reuters)