March security update for Nexus 6 pulled due to Android Pay issue
As a result, you won't find the March security update among the Nexus Factory Images or Nexus OTA web pages. After all, who would want to install an update that makes their device less secure?
According to a tweet from the @googlenexus Twitter account, Google is aware of the situation and is investigating. Besides the complaints found on Reddit, there is an official issue tracker number (240065) found on the Google Code website. Check it out by clicking on the sourcelink.
source: GoogleCode, @googlenexus via AndroidPolice