A controversial change in Maryland Gov. Martin O’Malley’s otherwise popular bill to expand early voting could lead to voter fraud and expose the state’s elections to cybersecurity threats, according to a voting group and election technology experts.

The provision, sought for more than a year by Maryland’s State Board of Elections, would allow any Marylander to receive a password by e-mail to download and mark a ballot at home before mailing it back to elections officials. But the problem, critics warn, is that the e-mail system lacks basic protections and there would be no signature verification or other means to ensure that the person for whom the ballot is intended is actually the person who casts it.

Experts have also warned that the proposed online ballot delivery system could be hacked on a massive scale because of a second and related vulnerability that still exists with the state’s new online voter registration system.

Maryland residents can register to vote online with a driver’s license number. But in Maryland, that number is a formula of a resident’s name and birth date that can be found online.

Rebecca Wilson, co-director of the nonprofit SAVE Our Votes, testified before state lawmakers Thursday that any hacker who pays $125 for Maryland’s publicly available database of voter records and who is adept at scouring Facebook or other social media sites for birthdays could easily assume voters’ identities and compromise a state election.

“By taking the voter history file, it’s pretty easy to see who votes and who doesn’t. A hacker could target those who don’t vote and request absentee ballots on the behalf of tens of thousands, and there would be no way for the State Board of Elections to determine that,” said Wilson, a chief elections judge in Prince George’s County.

Asked by lawmakers about such a scenario, Ross K. Goldstein, deputy administrator of the elections board, acknowledged an ongoing vulnerability in the state’s new online voter registration system because of its reliance on driver’s license numbers.

But he said the board was monitoring the system for suspicious behavior and in coming months would begin requiring registrants to answer additional questions with personal information to confirm their identities before creating or altering a voter registration file.

Goldstein dismissed Wilson’s broader complaint about the move toward online ballot marking, suggesting that she and other critics want the state to return to paper-only balloting.

“I believe technology can solve problems, and there are steps that we definitely can, and plan to, take to mitigate the risks,” he said.

But Wilson warned that he state’s proposed system could expose voters’ ballot preferences to online intruders.

In Maryland, any resident can choose to voteabsentee, and those who select to receive a ballot over the Internet would have the option of marking their preferences electronically on their computer or printing out the ballot and marking their selections by hand.

Selections that voters make online would be embedded in a bar code that would appear once the voter prints the ballot. Whether marked by hand or online, the ballot would still have to be returned by mail. But Wilson warned that online snooping software, such as that used to monitor employees at the U.S. Food and Drug Administration, could surreptitiously capture a voter’s selections.

Wilson and other local elections officials also warned of untold new costs and potential delays in counting the new ballots, because election workers would still have to reprint each ballot on a type of paper that can be read by electronic vote counters. Each ballot would also have be verified by hand for security reasons.

Goldstein noted that the system is being used successfully to deliver ballots online to Maryland’s small percentage of military on active deployment and voters overseas.

The National Federation of the Blind, United Seniors of Maryland and the Maryland Disability Law Center were among several groups testifying forcefully in support of the online system.

“It is imperative that the legislature modify the absentee ballot process so that it can truly be accessed and utilized by all Maryland voters,” said Alyssa R. Fieo, the law center’s legal advocacy director. By voting at home, she said, online balloting will allow those with disabilities “to vote privately and independently and in the manner in which they have chosen.”

However, Del. Don Dwyer (R-Anne Arundel) questioned how, without signature verification or other means, the state could be so sure that a ballot was not filled out by a relative or someone else. Unlike some states that have gone entirely to mail-in balloting, Maryland does not verify signatures on any absentee ballots. In November, 5 percent of voters cast absentee ballots; 16 percent voted early at polling places.

The bulk of the bill by O’Malley (D) is aimed at eliminating long lines that have plagued voters in the two statewide elections since Maryland began early voting.

His bill would increase the number days for early voting, its number of early voting sites and for the first time, allow residents to register on the same day they cast a ballot.

House Ways and Means Chairwoman Del. Sheila E. Hixson (D-Montgomery), said she was in strong support of the bill but concerned about the online portion.

“How we handle this cyber stuff right now is hard to legislate,” she said. “We would like to see it a little tighter.”

Last fall, Alex Halderman, David Jefferson, and Barbara Simons, researchers at the University of Michigan, the Lawrence Livermore National Laboratory and a former president of the Association for Computing Machinery, respectively, wrote to Maryland elections officials urging them to take immediate steps to better protect the state’s online voter registration system.

The three sent a follow-up letter Wednesday, saying they were concerned that Maryland’s system remained “up and running and open to large-scale, automated registration fraud.”

“Maryland’s elections would be even more at risk if this vulnerable voter registration system were coupled with on-line delivery of ballots,” they wrote, “especially since Maryland does not compare absentee ballot signatures to the signatures of record.”