I had the same problem and simply logged onto the gateway via the xfinity mobile app, reset the SSID and password and then log on to your desktop or laptop computer, open the Windows Registry, search/find "utopia.net", right click on it and delete. Then, make sure you 'edit' and 'find next' to be sure and get rid of all traces.
You can actually delete it from the registry first if you want and then reset the gateway SSID and password. This worked like a charm for me and haven't had any problems since. Calling comcast is a waste of time as they will do nothing nor admit that this is an issue with their modems. Their techs are generally trained to troubleshoot connection problems, and not malware problems. Also, I highly doubt there are any anti-malware programs out there that will fix it because it's not your normal malware/hijack.
Hope this helps.
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