Apple may tout marquee features such as multitasking and a smarter Siri as the best reasons to update iPhones and iPads to iOS 9, but your own peace of mind may be the best reason to click on Software Update. Not only does the new version of the OS allow for harder-to-crack 6-digit PINs, but two-factor authentication now has been built in.
Annoyingly, though, those who currently use two-factor authentication for iOS and OS X devices will need to re-enroll. According to Apple, "The current two-step verification feature will continue to work separately for users who are already enrolled."
iOS 9 can be installed on iPhones dating back to the 4s, iPads dating back to the iPad 2 and the iPod Touch dating back to the 5th generation.
Apple has also patched a bug that let advertisers poke around in iOS devices to see which programs were installed. Some prying companies used this to target users with more focused ads.
iOS 9 sees plenty of fixes in WebKit, the rendering engine that powers mobile Safari. A total of 33 Common Vulnerabilities and Exposures (CVE)-class bugs were fixed in WebKit alone, and we're looking forward to much safer Web browsing.
Another now-destroyed bug was found in Apple Pay, Apple's NFC payment process; the flaw allowed some payment cards to leave transaction data with the terminal being used. That was a big problem for Apple, which touts Apple Pay as beneficial to user privacy and anonymity.
Even Siri had a security problem. The personal assistant was caught reading notification data to anyone who had physical access to a device, even if the phone was locked. That, according to Apple, has been fixed in iOS 9.
In the past, Apple had trouble with major updates of iOS, including one that disabled cellular reception. This time around, there do not seem to be as many problems, although some users had problems getting the update to download at all. This improvement in reliability may be due to the public beta-testing of iOS 9, which let user help iron out kinks.