---
schema_version: "secwatch.filing_event.v1"
accession: "0001437749-25-019008"
form_type: "8-K"
ticker: "MNSB"
cik: "0001693577"
company_name: "MainStreet Bancshares, Inc."
filed_at: "2025-05-30T23:59:59+00:00"
generated_at: "2026-05-20T04:32:12.065072+00:00"
event_type: "cyber"
sentiment: "negative"
materiality_score: 0.35
calibrated_materiality_score: 0.35
confidence: "high"
source: SEC EDGAR
---

# MainStreet Bancshares discloses data security incident via third-party vendor affecting 4.65% of customers

## Summary
- Incident discovered in March 2025 when an outside vendor to the core bank was compromised.
- Company's own IT systems were not compromised; no unauthorized transactions or fund transfers occurred.
- On April 28, 2025, vendor's compromised system was found to include PII on ~4.65% of customers.
- Regulators notified; affected customers notified on May 26, 2025, with monitoring tools provided.
- Company states incident has not materially impacted operations, financial condition, or reputation.

## SEC filing metadata
- accession: 0001437749-25-019008
- form_type: 8-K
- ticker: MNSB
- cik: 0001693577
- company_name: MainStreet Bancshares, Inc.
- filed_at: 2025-05-30T23:59:59+00:00
- event_type: cyber
- sentiment: negative
- materiality_score: 0.35
- calibrated_materiality_score: 0.35
- confidence: high
- sec_items: 8.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1693577/000143774925019008/0001437749-25-019008-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1693577/000143774925019008/main20250328_8k.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001437749-25-019008
- JSON: https://secwatch.observer/filing/0001437749-25-019008.json
- Plain text: https://secwatch.observer/filing/0001437749-25-019008.txt

This AI-assisted summary is a reading aid. Review the linked SEC EDGAR filing before relying on any specific claim.