A programming error in GitHub's system led to the inadvertent exposure of data from 156 private repositories, including one belonging to GitHub, due to a bug in their deployment that misrouted Git requests. This issue was not a result of an external attack but rather an internal fault in the connection handling code of their Rails application, affecting a small percentage of Git operations. The bug caused some Git requests to retrieve data from incorrect repositories, leading to potential disclosure of repository histories, although no data integrity issues were found with Git pushes. GitHub has notified affected users and is taking preventive measures by updating its database driver and connection pool management to prevent future occurrences. The company emphasizes the importance of trust and is committed to learning from this incident to enhance its systems and processes.