Google has really improved as of late on Android's security overall. The improvements have come by way of monthly security patches. If you keep your phones stock you can easily update your device as the new updates release. If you have a custom recovery installed things can be a bit more difficult.
Even with a custom recovery installed you can easily update with ota.zip files. Joe Kester aka "WindroidGuy" has put together a full out repository of Nexus OTA files, and hes keeping it updated! As new updates release the site linked below will be updated. If you own a Nexus device you will want to be sure to bookmark this site.
via AndroidOTA.link