Soldato
http://support.apple.com/kb/HT6281 said:About the update
The OS X Mavericks 10.9.4 Update is recommended for all Mavericks users. It improves the stability, compatibility, and security of your Mac.
This update:
Fixes an issue that prevented some Macs from automatically connecting to known Wi-Fi networks
Fixes issue causing the background or Apple logo to appear incorrectly on startup
Improves the reliability of waking from sleep
Includes Safari 7.0.5
For detailed information about the security content of this update, see Apple security updates.