There's something very obnoxious about the newly implemented ads that came with the Xbox Live Dashboard update. Not only are Xbox 360 owners made to pay a yearly subscription for the service, they are now subject to intrusive ads that do little more than clog the experience—hardly fair, considering you have to pay money to use it in the first place.
If you'd like to get rid of those ads, it's possible to do so without too much hassle, and you won't even void your Xbox 360 warranty. Here are the steps you'll need to take:
1) The first thing you'll need to do is to sign up for an OpenDNS account.
2) Add a network for your current IP address. This may prove to be a hassle if your IP is dynamic, but it shouldn't pose any problems for anyone with a static IP address.
3) Go to Advanced Settings and next to "Domain Typos," hit the "Enable typo correction" box if it isn't already checked and hit Apply.
4) Go to Web Content Filtering, set the filtering level to "None," and under "Manage individual domains," add "rad.msn.com" (without quotes) and select "Always block" and then click "Add domain."
5) On your Xbox, go to System Settings -> Network Settings -> (your connection) -> Configure Network -> DNS settings -> Manual, and enter the OpenDNS IP addresses for the primary and secondary DNS servers: 208.67.222.222 and 208.67.220.220.
6) You'll have to clear your hard drive cache before ads disappear entirely. To do so, go to System Settings -> Storage -> Hard Drive -> press Y -> Clear System Cache. Doing so will force you to re-download any title updates for your games, but at least you won't have the ads to bother you any longer.
Be sure to grab the OpenDNS updater if you're on a dynamic IP.
Source: Reddit