Hot on the heels of releasing iOS 7.0.6, Apple has also released iOS 6.1.6 (build number: 10B500) for iPhone 3GS and iPod touch 4G for bug fixes.
iOS 6.1.6 fixes the following security issue:
Data Security
Available for: iPhone 3GS, iPod touch (4th generation)
Impact: An attacker with a privileged network position may capture or modify data in sessions protected by SSL/TLS
Description: Secure Transport failed to validate the authenticity of the connection. This issue was addressed by restoring missing validation steps.
Here are the direct download links for iOS 6.1.6:
iPhone 3GS
iPod touch 4G