This detects the http-rpc-epmap service by connecting to the port 593 and processing the buffer received. This endpoint mapper provides CIS (COM+ Internet Services) parameters like port 135 (epmap) for RPC.

Deny incoming traffic from the Internet to TCP port 593 as it may become a security threat in the future, if a vulnerability is discovered. For more information about CIS: http://msdn.microsoft.com/library/en-us/dndcom/html/cis.asp