The firm leading a widely criticized, Republican-backed audit of election ballots in Arizona has received $5.7m in donations, the majority from supporters of Donald Trump, it revealed on Wednesday.

Cyber Ninjas, a Florida-based company with no prior experience in election audits, said it had received $3.25m from Patrick Byrne, the CEO of the furniture sales company Overstock, who has falsely described the 2020 election as “rigged”, with more money pouring in from figures who have peddled lies about the legitimacy of the vote.

The firm was hired by Arizona’s GOP-led senate to review the 2020 election in Maricopa county, home to Phoenix and most of the state’s Arizona’s registered voters.

Doug Logan, Cyber Ninjas’ CEO, released the detail on the company’s donors after the congressional House oversight and reform committee demanded the information, citing the Cyber Ninjas’ “lack of experience in conducting election-related audits” and “sloppy and insecure audit practices”.

The Arizona senate allowed Cyber Ninjas to collect private donations even though the company was being paid $150,000 for the audit.

Information from Cyber Ninjas showed that it has collected $976,512.43 from America’s Future, a rightwing non-profit organization chaired by the Trump ally and QAnon devotee Michael Flynn. The company received $605,000 from Voices and Votes led by Christina Bobb, a correspondent for the hard-right media organization One America News Network.

Defending the Republic, a group led by Sidney Powell, Trump’s attorney who has filed a number of baseless lawsuits challenging election results, gave $550,000.

Logan has fought to keep the funders of Cyber Ninjas secret, though he acknowledged at the beginning of the audit that his $150,000 contract with the Arizona senate would not cover the cost of the work his company had been hired to do. He released the figures on the deadline for him to voluntarily comply with Congress’s request for information.

The ballot review has been derided as a “sham audit” by Democrats, and even criticized by GOP leaders in Maricopa county. It has been condemned by election experts, who have said that officials are not using a reliable methodology.

On Wednesday the review was subjected to further scrutiny when Ken Bennett, the former Republican secretary of state and the senate’s unpaid liaison to Logan and the audit contractors, said he planned to quit.

Bennett is the only audit leader with substantial experience in elections, and his departure threatened to even further erode any legitimacy the unprecedented partisan post-election review claimed to have.

Late on Wednesday Bennett reversed course, however, telling Associated Press he had reached an agreement to stay on.

The Associated Press contributed reporting