TOPEKA — Partial Social Security numbers of nearly 1,000 Kansas voters were released publicly by Florida after Secretary of State Kris Kobach's office provided the data as part of a program that looks for double voter registrations.

Kobach called the disclosure unfortunate, but defended the program, called Crosscheck, as key to his prosecutions of voter fraud. He has obtained nine convictions since gaining the ability to prosecute in 2015.

"It is absolutely essential. The Crosscheck provides the first piece of evidence that a person may have voted twice," Kobach told the Wichita Eagle.

"If the Crosscheck program were to go away, then we would be unable to catch virtually all of the double voters," he said, contending "there are thousands of them across the country."

But a Democratic candidate entered the race to replace Kobach on Monday, criticizing Crosscheck and saying he wants Kansas to leave the program. Lawmakers also are pressing Kobach's office for assurances Crosscheck's data is secure.

Other states are expressing concerns about their participation as well.

Crosscheck shares voter data among 28 states looking for possible duplications on the voter rolls. The program predates Kobach, but Kansas hosts it and Kobach has been its most prominent defender.

Florida shared the last four digits of the Social Security numbers of 945 Kansas voters with a Kansas resident in response to an open records request. Anita Parson, a suburban Kansas City resident opposed to Crosscheck, filed requests seeking information about the program.

When Florida provided Parson with documents last year, she said she was surprised to find the names and partial Social Security numbers of voters among them.

"Absolutely, it was (shocking). Especially since I didn't even ask for data. It just was a kind of incidental attachment," Parson said.

Florida has had the data since 2013, when the Kansas Secretary of State's office in an email sent Florida the names and partial Social Security numbers as part of the Crosscheck program.

Parson gave the data to the group End Crosscheck, which mapped it (they redacted the Social Security numbers). The map shows the individuals whose Social Security information was compromised come from across Kansas.

Florida's Department of State said Friday it has no reason to believe the information of individuals had been misused. It said it would offer identity theft monitoring to affected voters and added it was reaching out to voters individually.

"That was a really unfortunate mistake by some person in Florida. Mistakes happen, and obviously they broke their own open records law by releasing some last four digits of Social," Kobach said.

Crosscheck is beginning to emerge as an issue in the race for secretary of state. Kobach is running for governor, and therefore won't run for re-election as secretary.

Brian McClendon, a Lawrence Democrat, announced his run for secretary of state Monday, saying Kansas should leave Crosscheck. The former Google and Uber executive said the state should instead use a program called ERIC, or the Electronic Registration Information Center.

More than 20 states participate in ERIC. Some states use ERIC and Crosscheck.

"The goal of the system is not flawed. The mechanism clearly is," McClendon said.

Rep. Keith Esau, an Olathe Republican also running for secretary, said he would continue Crosscheck if elected. He said someone in Florida didn't properly process the open records request.

"But the email that was sent to them, that happened several years ago and that will not happen again," Esau said referring to the Kansas email to Florida that contained voter information.

ERIC is run by a nonprofit corporation, while Crosscheck is run out of Kobach's office and has no dedicated staff members.

Kobach said ERIC doesn't show potential double votes, unlike Crosscheck.

"ERIC only shows you, potentially, if someone is registered twice," Kobach said.

Earlier this month, the Illinois State Board of Elections voted to not send data to Crosscheck. A bill in the New Hampshire legislature would pull that state out of the program.

Rep. Brett Parker, D-Overland Park, said he didn't think Kansas could continue Crosscheck not knowing what the financial liability is, what the security risks are and what other states are doing with the data.

"I think at the very least, we need to solve all of those issues," Parker said. "To me the obvious solution is that we drop the program and we enroll in the alternative program that actually functions the way it's supposed to, which is the ERIC program."