Recent thefts of credit card data in Boston have affected hundreds of people, including an estimated 300 convention-goers. Police suspect that local businesses’ systems were hacked by thieves.

Some conference-goers who visited Beantown this fall got a little more than they bargained for later on their credit card statements.

In October, the American Society of Human Genetics hosted its annual conference at the Boston Convention and Exhibition Center in the city’s Seaport area. Since then, some 200 attendees have reported unauthorized charges to their credit cards, according to The Boston Globe. Weeks later, the American Public Health Association held its conference at the same South Boston facility, and about 100 attendees have since reported finding similar fraudulent charges.

It isn’t known how or where the data thefts occurred, but police note that the scope of the crime suggests the thieves hacked into the computer system of one or more Boston businesses, Boston Police Detective Steven Blair told the newspaper. The state’s attorney general’s office and the U.S. Secret Service are now aiding in the investigation.

On Thursday, the Boston Police Department said that the conference attendees are not the only ones affected and that interviews with credit card companies suggest “hundreds” more could be affected. “It’s extensive,” Blair told the Globe. “It’s not just focused on the Seaport area.”

This news comes weeks before the Professional Convention Management Association will host its Convening Leaders conference at another Boston site—the Hynes Convention Center.

The Massachusetts Convention Center Authority, which oversees both convention centers, maintains that no breach occurred within its facility. “After running internal checks and working with our customers, we found that no alleged theft occurred in any MCCA facility and [it] appeared to occur at bars and restaurants across the city,” said authority spokesman Mac Daniel, in a statement to the Globe.

Boston Mayor-elect Martin J. Walsh vowed that the police and convention center will “get to the bottom of it,” according to the Globe. “I’m not worried about Boston. Boston is a safe city,” said Walsh.

Meanwhile, the MCCA also sought to reassure future convention planners that it would work to assist visitors with such issues in the future.

“Though the credit card thefts occurred outside of our buildings and outside of our control, I would like to personally assure our future clients and attendees that the MCCA, our hospitality community, and the Boston Police Department have always been deeply invested in the overall safety of conventioneers that do business in our city and will continue to be vigilant in this area,” MCCA Executive Director James E. Rooney said in a statement.

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