Microsoft has announced an ambitious effort to make voting secure, verifiable and subject to reliable audits by registering ballots in encrypted form so they can be accurately and independently tracked long after they are cast. Two of the three top U.S elections vendors have expressed interest in potentially incorporating the open-source software into their voting systems. The software is being developed with Galois, an Oregon-based company separately creating a secure voting system prototype under contract with the Pentagon’s advanced research agency, DARPA. Dubbed “ElectionGuard,” it will be available this summer, Microsoft says, with early prototypes ready to pilot for next year’s U.S. general elections. CEO Satya Nadella announced the initiative Monday at a developer’s conference in Seattle, saying the software development kit would help “modernize all of the election infrastructure everywhere in the world.” Three little-known U.S. companies control about 90 percent of the market for election equipment, but have long faced criticism for poor security, antiquated technology and insufficient transparency around their proprietary, black-box voting systems. Open-source software is inherently more secure because the underlying code is easily scrutinized by outside experts but has been shunned by the dominant vendors whose customers — the nation’s 10,000 election jurisdictions — are mostly strapped for cash. None offered bids when Travis County, Texas, home to Austin, sought to build a system with the “end-to-end” verification attributes that ElectionGuard promises to deliver. Two of the leading vendors, Election Systems & Software of Omaha, Nebraska, and Hart InterCivic of Austin, Texas, both expressed interest in partnering with Microsoft for ElectionGuard. A spokeswoman for a third vendor, Dominion Voting Systems of Denver, said the company looks forward to “learning more” about the initiative.