It's been a while so I might be some versions behind but if I'm not mistaken SSL decryption is needed to block ultrasurf.
Then you can block the Ultrasurf app by policy.
Best practice to also block unknown-tcp.
So its not seeing the application correctly? Perhaps that is a question for TAC support? Have you added a rule that blocks the ultrasurf application prior to all your other policies to see if it will block it? Or maybe you can use the URL filtering to block Category: proxy-avoidance-and-anonymizers?
Just a few thoughts.
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