Major American banks and mortgage lenders were actively assessing their potential exposure following a significant data breach at SitusAMC Group Holdings, LP, a technology vendor serving real estate financiers. SitusAMC disclosed on Saturday that its systems had been compromised, leading to the unauthorized acquisition of client data, which included sensitive information such as accounting records and legal agreements.

The company first detected the intrusion on November 12 and has since been working rigorously with external cybersecurity experts and federal law enforcement to determine the full scope and impact of the breach. SitusAMC issued letters to its customers on Saturday, assuring them that operations remained fully functional and that the breach had been contained, notably without the involvement of encrypting malware.

Among the prominent financial institutions that received notification were JPMorgan Chase & Co. and Citigroup Inc. While representatives from both banks declined to comment on the specific implications for their operations, the Federal Bureau of Investigation (FBI) confirmed its awareness of a cyber incident involving a third-party provider within the financial services sector. The FBI, however, stated that no operational impact on banking services had been identified.

SitusAMC Chief Executive Officer Michael Franco reiterated that the breach was contained and emphasized the company's focus on meticulously analyzing any potentially affected data. Franco assured that updates would be provided directly to clients as the investigation advanced. The firm had begun notifying customers last week and specifically informed all residential mortgage customers about the potential for impact, underscoring the ongoing efforts to fully understand the extent of the compromised data.