A MAJOR security flaw has been found in some core Apple software. The flaw affects both iOS devices like iPhones and iPads, and also OSX apple products like mac laptops and desktop computers.
This flaw lets hackers see things you transmit over the internet using the Safari web browser, including passwords, financial transactions etc. Therefore, it's VERY IMPORTANT to fix on your Apple devices.
PLEASE MAKE SURE TO BACKUP YOUR DEVICE BEFORE DOING THE UPGRADE.
If you need help, please contact the Helpdesk.
The patch for mac OSX has not yet been released. You should use only Chrome or Firefox for web browsing in the meantime. Do not use Safari until apple fixes this problem.
If you're curious about the security flaw, here is a good link to the story: