You're talking about something that's actually quite controversial, something called "domain hijacking" in the trade. The basic idea is that the Domain Name System (DNS) works by you entering a domain name address, then your computer asking the DNS Server if it knows the IP address associated with that name. If it does, it sends that back and all is well. If it doesn't, it asks what's called an "upstream" or "root level DNS server" if it knows the number associated with that name. This query can bounce up a few levels in an extreme case (especially for overseas domains) but generally it's all resolved in fractions of a second.

The situation arises when the DNS server says "jeez, I dunno" when asked "what's the IP address associated with domain XYZ.COM?" At that point, it should simply return that error condition to your computer and then your Web browser can determine what action to take (some actually offer up suggested alternatives or try to fix misspellings). Comcast, however, recognized a revenue opportunity and instead of returning the error code, actually returns a page that indicates your domain couldn't resolve, a bunch of ads and the result of searching for your specified domain on Yahoo.

Here's an example, when I tried to go to the nonsense domain address of www.fdsafsafds.com:

What I'm thinking is if I click on these adverts and generate some revenue for Comcast, shouldn't the company credit me a few pennies on my bill, so that if I constantly hit this page and constantly clicked on advertisements, I'd get a significant break on my bill? That's not how they think about it, however, so instead let me show you how to disable it.

The first step is to go to your Comcast account at Comcast Customer Central. Log in, click on the "Users & Settings" tab and you'll see something like this:

Totally overwhelming, I know. Let me zoom in on the section labeled "High-Speed Internet Settings", however, and you'll be able to see the option you need to change:

The failed domain redirection goes by the pleasant name of "Domain helper" and as you can see, I have mine enabled just as I'm sure you have yours set to "ON". To change it, click on the "Edit" button to the immediate right and a window will pop up with the possible settings:

Fair enough. Click on "Disable Domain Helper" and then click on "Save" to make it actually change in the Comcast system itself.

Now I do another search for the "www.ffsafsafas.com" domain and this time it's Safari that gives me a more soothing to the eye error:

Follow my steps and you'll have things back to the way you prefer in no time!