To be perfectly clear: It is not hijacking when you are sending them queries for which you should have no reasonable expectation that they service. If you are actually a Level 3 customer, call your sales rep, but I believe this is only for non-customers.
Yes, it can screw up caches and return unexpected content.
Inserting an ad where an error should be is detrimental because the implementation often break standards endpoint and intermediate apps depend on (http code, DNS query answer/s). An app that was expecting just JSON now dies in some horrible (maybe silent or end-user confusing stacktrace) way.
> Yes, it can screw up caches and return unexpected content.
Then the cache is broken. Obviously not getting a response is going to confuse things, but there is a way to send back REFUSED without giving a positive or negative answer.
Take HN's authoritative DNS server and ask it for information on yahoo.com.
They are perfectly right to refuse service to non-customers, but I think it's bad network practice (legally right or not) to return incorrect information.
and one of them is returning bogus junk. why should they (the NSP) care? especially if you aren't paying them for a network service? it's not hijacking -- 4.2.2.2 isn't a public resolver and never was. it just happened to become one.
I'd say they should care because the Internet only survives through cooperative effort. Breaking something so they can pocket money is greedy and dickish.
But if they are being jerks rather than just being thoughtless, then maybe that isn't enough. In which case, my fallback answer is "bad PR". It would have been easier for them just to deny service to anybody they didn't want to serve. They went to a lot of trouble break something in a profitable way. To me, that says they might not be a trustworthy vendor, and thousands of nerds are now aware of that.
I'm going to go sit in your car and wait for you to start driving to the store, then start screaming bloody murder that you are hijacking the car and not taking me to work.
This like you ask me for the nearest mac donalds, I ask to my buddy and he tells me in this place there are no mac donalds. So I refer you to my own restaurant telling you it is a mac donalds. My restaurant, of course, does not serve burger and all the meat is crap.
EDIT: By the way, this is the actual company operating the "service" behind the scenes for Level 3 http://www.xerocole.com/searchguide/