If you are wondering what Microsoft Advanced Threat Analytics is then take a look at these two videos.
To learn about how the product works then have a look at:
If you are looking to purchase the product today have a look at:
For most most smaller customers the best way to get the product today is via the:
However, it is also expected to be part of the new E5 Office 365 license that will be available shortly.
-- Update --
I found today that if you go to the Add-ons for your Office 365 subscription you can purchase Exchange Online Threat Protection as a stand alone extra to your existing Exchange Online mailboxes. That make it easy to quickly and easily increase the security of your email protection with Office 365.
For more details see: