Mainstreet Credit Union Discloses Data Breach Affecting 4,123 Individuals Mainstreet Credit Union, a member-owned financial institution based in Lenexa, Kansas, reported a data breach impacting 4,123 individuals across the U.S. The incident was detected on January 19, 2026, when the credit union’s Managed Security Operations Center identified suspicious activity in an employee’s email account. The compromised account was secured immediately, and an investigation was launched. On January 22, 2026, Mainstreet Credit Union engaged law firm Baker & Hostetler LLP and forensic firm CRA to assess the breach. The investigation confirmed that an unauthorized actor accessed the Microsoft 365 email account between January 12 and January 20, 2026, though the exact emails and attachments viewed could not be determined. A full review of the account’s contents, completed on April 6, 2026, revealed that sensitive personal data potentially including Social Security numbers, names, financial account details, and driver’s license numbers was exposed. The breach was disclosed to the Indiana Attorney General on May 4, 2026, with affected individuals notified the same day. In response, Mainstreet Credit Union is providing 12 months of complimentary identity monitoring through Kroll, including credit monitoring, fraud consultation, and identity theft restoration. Affected individuals must enroll by a specified deadline using a membership number provided in their notification letter. A dedicated support line (844-403-4628) has also been established for inquiries.