As many as 383 Medicaid enrollees in Maryland received welcome packets in the mail this month that contained the names and birth dates of strangers, health officials announced Sunday evening. They blamed the mix-up on a “programming error” caused by the chief IT contractor hired to build a health-insurance marketplace for the state.

Officials at the Maryland Department of Health and Mental Hygiene said they learned of the problem Friday after a customer contacted a Medicaid enrollment broker and reported receiving the wrong packet in the mail.

The enrollment packets are automatically assembled by pulling names, addresses and other information from a database of Medicaid enrollees, said Dori Henry, a spokeswoman for the Maryland health exchange. Often the problematic packets had the correct name of the policyholder, but the incorrect names of dependents.

The packets contained names, dates of birth and Medicaid ID numbers, officials said, but not Social Security numbers, financial information or medical information. An initial investigation found that the error affected up to 383 households with 1,078 individuals.

More than 120,000 Marylanders have newly enrolled in Medicaid for this year, many more than the state had projected. About 93,500 of those people were automatically enrolled when Medicaid was expanded in Maryland, and the rest went through the exchange.

Despite the incorrect packets, officials said those affected have active Medicaid coverage and can access services.

State health officials blamed the packet problem — which they say has been fixed — on Noridian Healthcare Solutions, a North Dakota-based IT contractor that Maryland hired to build its health exchange.

Noridian’s president and chief executive, Tom McGraw, said in a statement Sunday night that he regrets the inconvenience Marylanders endured. But McGraw said his company provided enrollment data that “the state previously tested and approved,” and the company was not involved in the printing or mailing of the enrollment packages.

This is the latest in a series of problems with the state’s dysfunctional health exchange , which crashed Oct. 1 on its first day of operation and has been plagued with problems ever since. Thousands of Marylanders in search of health insurance through the program have been stymied by frozen accounts, incorrect information and error messages. Some people who encountered problems with the site were even instructed to call a toll-free phone number that connected to a pottery supply shop in Seattle, the Baltimore Sun reported this weekend.

The packet mix-up raised questions about the security of information given to the health exchange — an issue that has worried some Maryland lawmakers.

“That’s a big concern of mine,” Del. Susan W. Krebs (R-Carroll) said last week during a briefing on the exchange. “Do we really feel confident that we have security measures in place for all of people’s information on all of these exchanges?”

Joshua Sharfstein, Maryland’s secretary of health and mental hygiene, said there are a “variety of security protocols and tools” on the site that are used to protect sensitive information, including Defense Department-level encryption. He also pointed out that because customers are no longer required to disclose pre-existing conditions, there is limited sensitive information in the system.

Upon hearing of the problem Friday, health officials said they stopped mailing out enrollment packages and instructed ­call-center employees on how to help residents who received the wrong information. The department plans to directly notify those affected and send them a correct enrollment packet this week.

Aaron Davis contributed to this report.