The US Department of Homeland Security notified 21 states on Friday that hackers targeted their election systems in 2016. None of the systems targeted were involved in tallying votes, and hackers were able to breach only a small number of networks. 

“As part of our ongoing information sharing efforts, today DHS notified the Secretary of State or other chief election officer in each state of any potential targeting we were aware of in their state leading up to the 2016 election,” Homeland Security spokesman Scott McConnell said in statement. 

Despite the news that vote counting systems seem to have been left unmolested, the notifications are one more piece of worrying news about the integrity of the US election system. The word came as the Department of Homeland Security continues its investigation into Russian government efforts to influence the 2016 presidential election. It also follows Facebook’s announcement Thursday that it will hand over to Congress thousands of election-related ads it believes Russian agents bought on its platform.

This isn’t the first time we’ve heard that hackers tried to get into state election systems before the 2016 presidential elections, which Donald J. Trump won amid fears that the government of Russian President Vladimir Putin was trying to influence votes. According to reports from last September, the US government informed election officials that hackers targeted the election systems of more than 20 states, and successfully infiltrated four. McConnell didn’t specify whether the hacking attempts reported today were different from the ones states heard about last year.

Arizona was among the states notified Friday. “DHS has let us know that the Russian government was involved in attacks on Arizona’s voter registration system in 2016,” a government representative said in a statement Friday.

The Associated Press also reported that Alabama, Colorado, Illinois, Maryland, Virginia, Washington and Wisconsin were among the states notified.