Another set of users were using the Yahoo web chat instead of doing what we are paying them for so I needed to block them also. There are a lot of useless and out of date messages posed about this but I finally figured it out, and the answer was close to what I did to disable gmail chat:
I setup my DNS with two primary domains for:
I then set a host record for those to go to 127.0.0.1
After that they couldn’t chat no more!