You have an option to download the Botnet list from a server.
To view the downloaded list
Navigate to Policy | Security Services | Botnet Filter.
Navigate to the Dynamic Botnet List tab.
You can manually download the list immediately by clicking on the Download button or after the download interval, the IP addresses from the list will start showing up on this page.
You also have an option to Flush the entries downloaded via Dynamic Botnet List Server.