In a number of documents relating to OCS and Lync, I've seen discussion of Spam over IM (SPIM). I've not really seen much decent discussion of it, other than it's an issue. Most of the material seems to assume you know all about SPIM.
For those that are not familiar, you might want to look at RFC 5039. This document provides some great background in SPIM and other malevolent IM related stuff.