Apple has released OS X Yosemite 10.10.4 with stability, compatibility, and security improvements.
The OS X Yosemite 10.10.4 update improves the stability, compatibility, and security of your Mac, and is recommended for all users.
This update: ● Improves networking reliability ● Improves Migration Assistant reliability ● Addresses an issue that prevented certain external monitors from functioning properly ● Improves the reliability of upgrading iPhoto and Aperture libraries to Photos ● Improves reliability when syncing photos and videos to iCloud Photo Library ● Addresses an issue that caused Photos to quit unexpectedly after importing some Leica DNG files ● Resolves an issue that could delay outgoing email messages in Mail ● Fixes an issue where a website could prevent the user from navigating away by presenting repeated JavaScript alerts in Safari