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The statement regarding IGMP establishing multicast groups is accurate because IGMP, or Internet Group Management Protocol, is specifically designed to manage the membership of Internet Protocol multicast groups. When a host wants to receive multicast traffic, it uses IGMP to join a specific multicast group. This process allows routers to learn which hosts are interested in receiving data from which multicast groups.

IGMP operates between the host and the router, allowing the router to keep track of group memberships and ensuring that multicast traffic is forwarded only to the hosts that have expressed interest in it. This functionality is central to multicast routing because it enables efficient use of network resources, minimizing unnecessary traffic to hosts that do not need to receive specific multicast streams.

In contrast, the other statements do not accurately reflect IGMP's purpose. For instance, IGMP does not manage data encryption, nor does it monitor network traffic or filter malicious packets. These tasks typically fall under different protocols and network layer functions. Thus, establishing multicast groups is indeed the primary and most relevant function of IGMP in the context of multicast routing.