If you know what the pattern are, you can add them to an "Identification profile" under Web Security Manager/Identification Profiles.
You'll create a profile, then add them using regex's under Advanced/User Agents.
And then use that profile in an access policy, and set that profile to block everything.
You could possibly just create a new policy, use your current identification policy, and just add the selection of User Agents there, and set it to block.
It sort of depends what other authentication you have going on, and whether you care about it for this policy.
