Illinois election officials believe their agency “very likely” was the target of a hack of voter data referred to in an indictment of Russian intelligence officers handed down Friday.

The indictment, part of special counsel Robert Mueller’s investigation into Russian interference in the 2016 presidential election, alleges that two officers of the Kremlin’s Main Intelligence Directorate (GRU) stole personal data from around half a million voters from an unnamed state board of elections.

Based on information in the indictment, Illinois State Board of Elections spokesman Matt Dietrich said Friday afternoon that officials believed the Illinois agency is the one identified in the indictment only as SBOE 1.

“We think it’s very likely that we are SBOE No. 1,” Dietrich said at a Springfield news conference. “We have not received any confirmation from the Department of Justice on that, but based on the circumstances described in the indictment, we think it’s pretty likely that that’s us.”

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“We never had anything on paper until today and even then we don’t have a firm statement from DOJ saying yes it’s us, although we think it’s more than likely that it’s us,” he added.

The dates reported in the indictment — a hack attempt launched in July 2016 and reported in August — match the reported dates of the attack on Illinois’s election system.

The number of voters whose information the indictment lists as compromised by the hack on SBOE 1  — “approximately 500,000 voters” — is substantially larger than the 76,000 voters identified and notified by the state in the wake of the attack. Dietrich speculated that federal prosecutors might be using a standard defined by the Federal Criminal Code, as opposed to Illinois’s Personal Information Protection Act, to reach that higher number.

According to the indictment, GRU officers Aleksandr Vladimirovich Osadchuk and Anatoliy Sergeyevich Kovalev began probing election infrastructure in the United States in June 2016. In July 2016, they allegedly identified a vulnerability in SBOE 1’s website and began to siphon off voter information.

The attack on the Illinois Board of Election overloaded its processors, alerting staff that something was amiss, the Chicago Sun-Times first reported last year. The vulnerable parts of the website were taken offline, and state and federal authorities were alerted to the hack.

According to the indictment, the hackers scrambled to cover their tracks after an FBI alert in August 2016 revealed that the FBI was aware of efforts to compromise election systems. The hackers nonetheless continued to look for vulnerabilities in other parts of the country, according to the indictment, looking at websites in counties in Georgia, Iowa, and Florida as late as October of 2016.

Democrats said Friday’s indictments should serve as another alarm bell.

“The 2018 elections are just four months away.  It is past time for President Trump, his inner circle, and Congressional Republicans to stop accepting Russian President Putin’s brazen denials and take this threat to our democracy seriously,” U.S. Sen. Dick Durbin D-Ill., said in a statement issued in response to the indictment.

In the Springfield news conference, Dietrich took responsibility on behalf of the board for the error that led to the hack, and pointed to subsequent efforts to harden the state’s elections infrastructure.

“We are doing everything we possibly can to make sure that this does not happen again. But every entity… has felt the same way, until [a breach] happens,” Dietrich said.

Dietrich also cautioned that there was no reason to believe that the integrity of the vote count — as opposed to voter information — had been compromised.

The indictment also alleges that Osadchuk and Kovalev compromised computers belonging to an unnamed vendor of voter registration software and sent emails bearing malware designed to look like they came from that vendor to election authorities in several Florida counties.

The conspiracy charges against Kovalev and Osadchuk represent a single count in an 11-count indictment against a dozen GRU officers for attempting to interfere in the 2016 presidential election in favor of Donald Trump. Since the Mueller investigation began in May 2017, 32 people have been indicted in relation to the investigation, five of whom have pleaded guilty.

Another part of the indictment alleged that GRU officers funneled data stolen from the Democratic National Committee and the Democratic Congressional Campaign Committee through a computer leased by the GRU in Illinois.