You can check the access log for the user agents you want to block, and configure for those.
To find user agent:
a) Browser to
GUI -> "System Administration" -> "Log Subscription" -> 'Access logs'
in the Custom fields
c) Submit and commit the changes
d) Grep or tail the access logs based on client IP address
e) The user agent string should be located at end of the access log line
Here is a close example, though this is doing authentication bypass:
Then instead of configuring for bypass authentication, configure an access policy that will block all traffic from this identity.
I hope this infomratiom helps you.
I found on some site for Flex Regex to do this to block Android.
Could add the iOS devices in a similar fashion, if you must get more granular, you can, just avoid version numbers as I assume they change often.
Oh the site is here: http://www.stratulat.com/Regular_Expressions_Flex.html