Which is why comcast goes to such great lengths to ensure they own as much of your network stack as they can - in my area at least, their support is capable of fully managing your router and WiFi remotely if you're leasing their equipment. I imagine this is a great boon for their ability to provide tech support (and includes a host of other "features" that don't serve direct customer needs such as a non-optional guest WiFi access point that any other comcast user can use).

This leads to fun tech support calls if you use your own equipment where you're basically proving to the support underling that you know how to run your equipment for the first 20-30 minutes before they take your issue seriously (yes, the modem light is green, yes, I've already power-cycled, yes, I'm testing on a wired connection, etc)