Each month, Google pushes out an update to their Nexus line of devices - as well as the Pixel C tablet - which has a slew of security fixes. Mostly it fixes vulnerabilities found in Android (which means it affects more than just Nexus, Android One and Pixel), Google does also make this code available to their partners about a month before it is rolled out to their own devices. Which Samsung posted their security bulletin for July 2016 earlier today, for their own devices. These security updates are pretty important for Nexus devices, seeing as there are plenty of vulnerabilities and exploits found in Android, and these updates will patch them up. This way nothing happens to your smartphone or tablet.
The devices being updated include the Nexus 5, Nexus 5X, Nexus 6, Nexus 6P, Nexus 7 2013, Nexus 9, Nexus Player and the Pixel C. Google has already posted the OTA files and factory images for these devices. So you are able to sideload the OTA file and be updated to the latest security patch - which there are two this month, July 1st and July 5th. Of course, the more important patch is the July 5th, as it has a few more fixes. Now, sideloading the OTA onto your device means that all of your files stay in place. So you don't need to worry about backing up your smartphone or tablet. If you go the route of flashing the factory image, you are essentially factory resetting your smartphone or tablet. It's a bit easier, sometimes, than flashing the OTA onto your device, but having to re-set up the device and download all your apps again, can be quite annoying.
Google has already released the security bulletin for this monthly security update, so if you are interested in seeing what has been patched in this update, be sure to check that out. There are quite a few vulnerabilities patched. While the updates are already available for Nexus, Android One and Pixel hardware, Samsung, LG and HTC should be pushing out their updates rather soon. As they are typically some of the first manufacturers to roll out their monthly security updates. And, luckily, they have been getting faster at rolling them out.