Arizona Secretary of State Katie Hobbs (D), the state’s chief elections officer, advised Maricopa County Thursday that it should replace all voting machines that were turned over to a private contractor for an audit of the 2020 presidential election, citing “grave concerns regarding the security and integrity” of the machines that make them unusable for future elections.

Hobbs’ guidance, outlined in a letter to county officials, is the latest fallout from a review of the election ordered by Republicans in the Arizona state Senate, who used a subpoena to order the county to turn over voting machines and nearly 2.1 million ballots to reexamine last fall’s vote.

The chief executive of the private company hired to conduct the audit has echoed false allegations that the election was stolen, and the process has been widely criticized by election experts as insecure and unprofessional.

Millions of dollars worth of Maricopa’s voting equipment used in the 2020 election — including nine tabulating machines used at a central counting facility and 385 precinct-based tabulators — were removed from a county facility and placed in the custody of Florida-based company Cyber Ninjas at the Arizona Veterans Memorial Coliseum for the review in late April.

In her letter, Hobbs wrote that after the machines were handed over to the Senate and Cyber Ninjas, “it is unclear what, if any procedures were in place or followed to ensure physical security and proper chain of custody.” She noted that no election official or observer was allowed to remain with the machines while Cyber Ninjas and its subcontractors examined them.

“The lack of physical security and transparency means we cannot be certain who accessed the voting equipment and what might have been done to them,” she wrote, advising that the county “should acquire new machines to ensure secure and accurate elections in Maricopa County going forward.”

Megan Gilbertson, a spokeswoman for the county elections department, said in a statement that the department was “working with our attorneys on next steps, costs and what will be needed to ensure only certified equipment is used in Maricopa County.”

“We will not use any of the returned tabulation equipment unless the county, state and vendor are confident that there is no malicious hardware or software installed on the devices,” she said.

A spokesman for Senate President Karen Fann (R) did not immediately respond to a request, nor did a spokesman for the audit.

The warning from Hobbs comes as election officials around the country contend with calls by Donald Trump supporters to launch their own Arizona-style reviews of the vote tallies in their communities.

Hobbs wrote that she did not make the costly recommendation lightly, but said she had consulted with experts, including at the Department of Homeland Security’s Cybersecurity and Infrastructure Security Agency, who agreed it was the right move.

An agency spokesperson said “CISA regularly provides security best practices to critical infrastructure partners. If it is determined that the chain of custody of critical systems have been compromised, the safest practice is to decommission and replace those systems. Election officials are best positioned to make that determination for their systems.”

Hobbs has previously expressed concern about the company’s methods, including frequently shifting rules for its count and ballots and computers left unattended on the counting floor.

In addition to examining voting machines from the county, which is the largest in Arizona, Cyber Ninjas has also been attempting to recount by hand all of Maricopa’s ballots, and has employed unorthodox examinations of the ballots using microscopes and UV lights.

Maricopa’s Republican-majority elected leadership this week expressed grave concerns about the Senate’s audit, calling it “spectacle that is harming all of us” and a process that was “encouraging our citizens to distrust elections, which weakens our democratic republic.”

Even so, Fann said this week that the recount, which was paused this week to allow local high schools to use the coliseum for graduation ceremonies, would continue next week.

Trump has been enthusiastically cheering on the audit, claiming it is the first step to vindicating his false claims that the election was stolen.