Don't get me wrong: I have referer traps, I just do not find them the most common reason for trapping.
If it really is a DSL range then it is no different from any other ISP's IPs being compromised. There are millions of compromised computers at any given time. For a few to be on a high-profile company's broadband system is no surprise. Although, in this case, ironic (if it really is compromised computers) in that MS almost certainly make the OS that accepted compromise.