You have to apply ACL's to block the traffic, trouble is figuring out what the traffic patterns are. Generally you would apply this ACL inbound on your inside interface, then put a "permit ip any any" at the end of it to allow everything else through.
Here's a good link for blocking most peer-to-peer apps, create your ACL's from this information:
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
[toc:faq]Introduction:This document describes details on how NAT-T
works.Background:ESP encrypts all critical information, encapsulating
the entire inner TCP/UDP datagram within an ESP header. ESP is an IP
protocol in the same sense that TCP and UDP are I...