Google is doing their part to make Android an even safer and more secure place for users of the platform with a recent update to the software which they'll soon begin pushing to devices. As of right now the OTA updates have yet to go out to Nexus devices for the latest build of the Lollipop software which is still Android 5.1.1, but is now up to build LMY481. Google has pushed the code to the Android Open Source Project though, and following the AOSP push Google has uploaded the factory images to the factory image database.
What this means is that anyone who is familiar with and capable of flashing the factory image to their device now has the ability to do so without having to wait for Google to push the OTA software out to devices. The process isn't as straightforward or as simple as tapping a notification to install a new update, but flashing the factory image also means users will be able to bypass any sort of waiting period. This time there is also a little more incentive to do so as this build is being pushed out as part of Google's monthly security updates program which has updates go out to Nexus devices on a scheduled monthly basis, an initiative which they announced earlier on in the year.
The more important reason though for people to install this update build as soon as they can is because it contains the patch for the recently announced StageFright vulnerability which has been in the news of late. Those who have even stumbled briefly onto any details regarding the StageFright bug should know it's a pretty serious deal. It's worth noting that it was already discovered Google would be rolling out fixes for StageFright to the Nexus 5 and Nexus 6 as of earlier this morning, but along with those two devices the factory images are also available for the 2013 Nexus 7, the Nexus 4, as well as the Nexus 9 and Nexus 10 tablets. If you're not capable of flashing the factory images, it might not be too long before Google sends out the official OTA software, in which case you can just tap to download and install as you would normally with any other update.