I don't think it's exclusively Comcast. But I have a lot of trouble with pop-ups and there's a virus or something of somekind I can't get rid of.
What happened this time is that uninstalling Firefox made it impossible for me to open Comcast without telling it to go to IE every time, even when I check the box for "always use this program."
What anti-spyware programs are you using? I might be able to recommend some that you're not running... and if you can find the file that hosts the virus, the way to get rid of it is to boot in safe mode, delete the file, and then delete it from the Trash. Often you can't delete a virus in normal running mode.
eww. that sounds nightmarish... and familiar. That is why PE lets me handle all the 'puter stuff anymore.