RCN in the past week has apparently been rolling out DNS hijacking. When you attempt to query a domain name that does not exist, their DNS servers respond with bogus responses that attempts to redirect your browser to their own search page. This is a horrible idea for many reasons like breaking various software, but they don't care because it brings them more revenue in advertising click-thrus.
If you are experiencing DNS hijacking with RCN, call 1-800-RING-RCN and complain about this. If they don't know what you are talking about, say you want to opt out of "Paxfire". Then file a complaint, because this is a horribly bad idea to inflict this upon customers by default.