In a shocking twist, a massive data breach has left sensitive customer information from several major U.S. banks vulnerable. Here are the key takeaways:

• The F.B.I. is now investigating the situation, highlighting the seriousness of the breach.
• JPMorgan, Citi, and Morgan Stanley are among the institutions affected.
• The breach is linked to a vendor's hack, raising concerns about third-party security measures.
• As banks scramble to assess the fallout, customers are left wondering about the safety of their data.

Here’s the full scoop.